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This presentation is delivered by the Stanford Center for Professional 

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Development. 

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So let's go ahead and get started with the actual content. And so today 

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is the day where we make a little bit of a transition. It's like one of our 

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transition points in life. It's kind of like coming to college. 

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And the transition point we make is you now come into the Java world, and you're like, 

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"But I'm still doing Karel." Yeah, in lectures, we're going to start to wave bye bye 

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to Karel and Karel's like, "Yeah, 

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I'll be there in your dreams when you're actually programming, right." So Karel's not 

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really gone until you're done with the Assignment No. 1. But now, we 

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take we sort of graduate into the world of Java and you'll actually see that a lot of things 

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that exists in Karel's world will come back because 

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we give them to in a gentle form in Karel's world and 

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then the Java world, they come full steam. So 

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before we dive into that, 

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I want you to get a little notion of the history of computing. Okay, and we'll go over this very 

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briefly, but computing actually has a very long history and it dates back about 

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4,000 years, okay. 

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So roughly 4,000 years ago, the first one we think of is computing 

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device was made available, but then you want to know what that was? 

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Advocates. 

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The first computing device allowed you to do some fairly 

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rudimentary arithmetic on it, 

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but it actually was something that allowed people to compute a lot faster 

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than they could by keeping track of stuff in their head. 

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The real sort of advances in what we think of as computing actually came 

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around in the 1800's. That was 

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someone by the name Charles Babbage. 

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Anyone heard of Charles Babbage, by the way, a just 

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quick show of hands. 

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We can just call him Chuck. He 

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was actually 

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a very well learned and well-known person in his day. He had the Lucasian 

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chair, 

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which is the same chair at university that actually Steven Hawking has now 

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that Sir Isaac Newton had at one point. So, 

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pretty smart dude, 

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and he came up with this notion of something called the Difference Engine, 

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which is a way of being able to automatically. And in those days, right, they didn't 

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have silicon. Well, they had silicon, but it was in the form of sand, 

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and they didn't have computers in the way we think of computers, so he wanted to 

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build a mechanical device like with real, actual, you know, mechanics and pieces of 

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woods that's been around, 

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and in his time, he thought is would be powered by steam, right, because this is sort of pre 

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thinking about electronic computers 

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that would do automated calculation. And he designed something 

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called the Difference Engine and then he designed something called the Analytic 

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Engine, which was supposed to be even more powerful, 

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and interestingly enough neither one of them was actually built during his 

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lifetime. 

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It turns out that years later, the difference engine was actually 

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built from a bunch 

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of wheels and rotors and stuff and now 

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the things, you know, that he would have liked to think of as the Analytic Engine 

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is actually these puppies. It actually turned in the 1800's; he had a lot of 

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the same ideas 

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that are in our laptops or in our computers today strangely enough. 

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But, so that's kind of where our computing we think of the notion of computing is 

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really coming from, 

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and it turns out the first programmer 

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was a woman by the name of Ada 

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Byron, actually Augusta Ada Byron and if the Byron looks familiar, too, is 

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because she was the daughter of Lord Byron, the English poet 

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and she was actually very taken by the designs of Charles Babbage's machines 

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and actually wrote programs. The machines were actually written to have sort of 

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cards, sort of 

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like the Jacard Loom if you've ever heard of the Jacard Loom, if you haven't, 

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it's not important, 

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that actually would have programs for the kind of computations that it would do 

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and see, she actually devised various programs 

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for Charles Babbage's Analytical Engine. And 

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you might be sitting there and you might think, 

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"But Marion, you've just told me that the Analytical Engine was never actually 

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built in their lifetime, 

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so what's she doing writing programs for a computer that doesn't exist," 

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and that's actually something that happens today. People write programs for 

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computers that don't exist and you might wonder 

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why. That's not a very good use of your time. 

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Well, guess what, 

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if the next generation of computers is going to come out while it's still being 

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designed before it's actually manufactured and built, 

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someone needs to figure out what kind of programs you want to run on that 

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machine, so there are actually programmers today who actually write programs for machines 

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that aren't built. And they simulate them by hand and they go through and try to 

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figure out what they would do and it's perfectly reasonably thing to do. 

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But as a result, Ada Byron is in some sense, the first programmer, 

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right, because she was actually writing programs for in some sense, a 

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general purpose computational device 

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over 100 years ago, which is kind of an astounding thing if you think 

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about it. 

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Now it turns out computing actually got its first real, you know, what we think 

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more closely of as computing devices 

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in the 1930's. I should put 19 here just so we're clear 1930's 

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and 40's, 

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they were sort of the first prototypes of electro mechanical computers that 

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were actually built at the time. There was a computer that was built at Iowa 

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State by Atanasoff and Berry. Their names are actually not well, they're 

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important if you're a lawyer because it turned 

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out there were actually lawsuits at the time by who patented it in the computer, 

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but we won't talk about that. 

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Started sort of in this era with sort of prototypes and then the 

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one machine you may have actually heard of by 1946, there was a 

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machine called ENIAC, 

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which was actually built by Elkhart and McCauley at U Penn 

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which was standard for, if I can remember this, for electronic, numerical integrator and 

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calculator. 

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And basically with one of these big things, you know, sat in a 

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big warehouse, a few tons, 

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but it actually did computational, 

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you know, the kinds of things we would think of as computation and it was 

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really in some sense the first large-scale electro magnetic computer 

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that we think about, again, you know, modular lawyers. 

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And then really it was in 1971, that the first 

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microprocessor came around, so we come to a fairly modern time, right, so it's not 

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all that long ago, like we're talking 36 years, 

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the microprocessors have actually been around. And so the first microprocessor 

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and one of the folks who was on that team who built the first microprocessor, Ted Hawk, is 

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actually Stanford alum, interestingly enough, it was built at Intel. The 

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Intel 4004 was the name of that microprocessor and at the time, no 

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one actually thought that 

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having a single chip microprocessor was going to be that interesting. He sort of designed 

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this thing and it was 

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originally going to be going over for use in some machine in Japan 

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and they were just going to give them some design and the patent for it and the 

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folks were getting like, "Well, we're not really interested. Yeah, sure it's an interesting 

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chip, but we're not really interested 

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in, you know, owning the patent. We don't think there's anything interesting 

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necessarily here," 

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and so they kind of ran with it and the rest is history, as they say. And as 

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you can imagine in the last 35 years or so, there's just been an astounding 

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amount of development in computing and computer science, right, 

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so really this field is like hundreds or thousands years old, if you think 

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about it, 

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but really it's kind of in your lifetime 

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that all the interesting stuff is really happening, 

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which is also why it's exciting to be alive now and be a computer scientist 

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because you're in this acceleration phase, right. 

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Think about what's going to happen, like all the stuff that happened in the last 36 

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years, 

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you're gonna be around to see the next 36 years and you're gonna be 

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doing the next 36 years, so that's just an exciting thing 

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that I think about. But 

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another thing that comes up when you think about this, what is computer science, 

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right, like why do we we've been talking about Karel programming and a lot of this 

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class we're gonna learn about software development and Java programming 

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and so a lot of people tend to equate computer science with programming and 

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they think, 

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"Well, why isn't a major just called, you know, computer programming and why is 

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there really a science to it in some sense." 

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That's something that people actually would use to debate. They don't really debate it 

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so much anymore. Is there a real science to computing 

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or is it just programming and in fact, 

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the difference between the two is that computer science or CS as we'll just 

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affectionately refer to it, 

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really is the science or in some sense, the study 

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of problem solving with computers, 

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and you don't need to write his all down; it's just for your edification, with 

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computers or I should say, computational devices. 

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Computational I'll even say methods because some people actually look at, you know, 

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theoretically what's possible without even necessarily thinking that 

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it's real life in hardware, right. Turns 

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out it actually surprises people there are some functions that you can prove 

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are not computable. I'm 

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like, "Really, you can?" Yeah, and it's good to know about them before you go and try to 

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write a program to actually compute them 

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because in theory they're not computable and you can prove that, and if you're 

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actually interested in that, take CS 103 or CS 154 and we'll talk about it all the time. 

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But that's really what the science is, 

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is thinking about problem-solving and the approaches to problem-solving, how you 

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analyze how efficient a solution is to a problem, how solvable it actually is, the 

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different approaches you take to it. 

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So, notice the word programming 

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doesn't show up here. 

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Programming is an artifact. It's something we do to realize that 

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particular problem-solving technique in a computer or some 

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computational method. 

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It's just something we do as part of the process, right. It's not what the whole 

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thing is really about. In some sense, 

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there is actually this famous quote that 

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computer science is just as much about programming as astronomy is 

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about building telescopes. 

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Right, astronomy is about far more than building telescopes. It's really sort of a science 

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of celestial bodies. 

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Telescopes is the mechanism by which you actually look at them. 

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Uh-huh, question in the back? 

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[Inaudible]. Well, if you think about computer engineering, part of it is just kind of a 

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definition that a particular school wants to have for it, right. 

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And some places actually our computer science program is in the School of Engineering. 

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Some places it's actually in humanities and sciences. 

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It depends on the view and it also depends on the particular program that's there, 

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so some places may actually 

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there's no way I'm gonna hit you in the back may just be training programmers, 

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right. And the science of computing is not what they're actually interested in, 

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and so it depends on the program, but we really think of the computer science as a science, and it's 

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an interesting philosophical argument. We can certainly talk about it more in class, 

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but I just wanted to kind of push on. All right, 

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so with that said, that's kind of the quick tour of a couple hundred years of 

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computer science history, 

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it turns out when we get into modern day, when we actually think about 

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computing, what does a computer really understand 

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and what are the programs that you write on it and how do they turn into something that 

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the computer understands. So it turns out that the computer actually understands zeros 

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and ones. 

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And so we like to think of that as binary, right. Binary is just a number system that 

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only has zeros and ones. It's base two numbers basically and that's all that computers 

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understands, zeros and ones on and off. 

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So how do we take these things like move or turn left and turn them into ones 

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and zeros, and so 

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there's something called machine language 

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that is what a computer understands or in some sense what the microprocessor 

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understands, right. The machine languages is defined by what chip you have inside 

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your computer. 

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That's eventually going to boil down into a bunch of ones and zeros. 

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People are real bad at writing ones and zeros in a form that computers can 

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understand. 

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So we program what's known as a high-level language, 

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okay. And there's all kinds of high-level languages, so one of the ones that you're gonna 

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learn in this class is Java and there's some other ones you may have heard like C 

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or C++ or Basic or Fortran or whatever the case may be. 

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These are all high-level languages, because they're at a higher level than what the 

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machine understands, 

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and so there's this question that's actually part of the science of computing is 

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how do you go from this high-level language 

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into something the machine understands, right. What is this translation process because there actually is some translation that needs to 

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happen 

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and this process going form the high-level language to the machine language 

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is something we refer to as compilation, 

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right. So compilation is something, strangely enough, that's done by a 

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compiler and Eclipse which you've been using this whole time is in fact a 

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compiler. It takes the instructions that you write in some high-level language 

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and converts them into some form that the machine understands. 

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Now it turns out that the process for doing this in some languages is actually 

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slightly different than other languages, so I want to show you 

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a quick little overview of how that looks in Java just so you can get a real 

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sense of what's going on between the time you write a program and the time the 

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machine executes it so you sort of understand it at a low level. 

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As programmers, you write what's called source code. 

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Know it, learn it, live it, love it. Source code that's what you're gonna write. When you 

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were writing Karel programs, you were writing source code. When you write Java, 

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you're going to write source code. 

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What the machine understands, these zeros and ones here, it's something that's called 

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objects code. 

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An object code is essentially just the low-level instructions, the machine 

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instructions 

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that the computer understands 

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and so 

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going from source code to object code is basically what the compiler does. It's the 

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translation from this to 

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this. 

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00:12:11,889 --> 00:12:15,600
Now in regular languages, that might look, if we got the overhead. 

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Is shouldn't say regular language. In some classical languages, 

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it might look something like this, you write some source code in what we refer to 

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as the source file. The source file is just a file 

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that contains source code. 

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00:12:26,340 --> 00:12:30,070
So you write your program that goes into some compiler, say Eclipse, which is 

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the compiler you're using 

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and what might come out of it is an object file because what is contained 

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in that file is just essentially object code 

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or in this case a bunch of zeros and ones that the computer understands. 

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And there might have been other programs that someone wrote along the way like 

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some libraries you might make use of like you did with Karel, right, all the 

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00:12:47,129 --> 00:12:49,730
basic Karel functionality might be in some other 

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library and so there's other files that contain object code 

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and all of this stuff gets linked together into one big set of object code 

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which we refer to as the executable or the application. 

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That's the thing that, say, when you double click on your word processor on your 

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computer and it runs, 

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you're running some executable file, which is just basically a file of a bunch of 

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ones and zeros that eventually 

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or as some time ago, someone wrote and source code and it got compiled down in this executable 

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file. 

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And for a lot of languages like C or C++, 

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this is the process that actually happens. 

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Now the people who did Java 

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thought of things slightly differently and here is kind of where things get funky 

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in Java, okay? 

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In Java's world, 

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00:13:29,169 --> 00:13:31,599
part of what's going on is actually 

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run on a virtual machine. What does that mean; it means you write some source file 

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in Java, okay, 

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that goes through some compiler and what comes out of it is not an object file, 

283
00:13:41,230 --> 00:13:43,220
but something called a class file. 

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It takes all of the high-level stuff that you write in Java or in this case, 

285
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you could say Karel because it's the same thing, 

286
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and turns it into 

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00:13:50,938 --> 00:13:55,740
some set of numerical instructions that are not yet ones and zeros that the computer 

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00:13:55,740 --> 00:13:59,430
understands but are some intermediate language, which is just a numerical language. 

289
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And sometimes you refer to this as Java bite code, 

290
00:14:01,999 --> 00:14:04,879
but the name is actually not important. It's some intermediate language, 

291
00:14:04,879 --> 00:14:08,889
and guess what, there's other classes just like there were before that contain 

292
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instructions in this intermediate language and those all get linked 

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together in some big file that we call a jar archive which just stands for jar just 

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means Java archive, strangely enough. 

295
00:14:18,480 --> 00:14:22,379
So it's actually redundant to say jar archive. People just do, but it means Java archive. All 

296
00:14:22,379 --> 00:14:23,960
right, 

297
00:14:23,960 --> 00:14:27,580
and then this whole thing is now instead of this intermediate language, it's 

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00:14:27,580 --> 00:14:30,470
something that neither the human really understands okay, there's a few humans in 

299
00:14:30,470 --> 00:14:33,490
the world that might and they're a little weird and we won't talk about them. 

300
00:14:33,490 --> 00:14:36,649
Most people don't understand this and the computer doesn't understand it 

301
00:14:36,649 --> 00:14:40,299
directly either. So you say, "Well, that's the most useless thing ever. Why would I ever 

302
00:14:40,299 --> 00:14:41,699
do that?" 

303
00:14:41,700 --> 00:14:45,310
These instructions go to something called the Java Virtual Machine, the 

304
00:14:45,309 --> 00:14:46,299
JVM, 

305
00:14:46,299 --> 00:14:49,879
and what the Java Virtual Machine says, it says, "Hey, guess what? 

306
00:14:49,879 --> 00:14:55,289
I'm going to be pretending like I'm a machine that understands this as my 

307
00:14:55,289 --> 00:14:59,259
object code. I understand this stuff as the basic language I speak, 

308
00:14:59,259 --> 00:15:02,950
and I take that and when I run it, I do something on your computer." 

309
00:15:02,950 --> 00:15:06,520
And you might say, "Why would you want to have this extra process?" 

310
00:15:06,519 --> 00:15:10,039
And the reason why you want to have this extra process is the fact that guess what, 

311
00:15:10,039 --> 00:15:13,939
in the world there's things like Macs and there's PCs and there's Linux 

312
00:15:13,940 --> 00:15:16,290
computers and there's all kinds of machines out there, 

313
00:15:16,289 --> 00:15:19,759
which means if you sort of do things in either the good old way or the bad old 

314
00:15:19,759 --> 00:15:20,929
way, 

315
00:15:20,929 --> 00:15:24,569
the compiler needs to understand what are the ones and zeros that your 

316
00:15:24,570 --> 00:15:28,080
computer speaks and the ones and zeros that a Macintosh speaks are different than 

317
00:15:28,080 --> 00:15:29,920
the ones and zeros that a PC speaks. 

318
00:15:29,919 --> 00:15:33,079
And they're different than the ones and zeros that the Linux machine speaks. 

319
00:15:33,080 --> 00:15:36,460
So the compiler needs to know all that if it's actually gonna generate this kind 

320
00:15:36,460 --> 00:15:40,019
of code for all of those different sorts of machines and most compilers don't. Most of the 

321
00:15:40,019 --> 00:15:41,230
time you've got a compiler that says, 

322
00:15:41,230 --> 00:15:44,490
"Hey I'm a PC compiler. I'm just gonna generate stuff for the PC and that's 

323
00:15:44,490 --> 00:15:45,830
all I do." 

324
00:15:45,830 --> 00:15:49,020
In Java's world, things are a little bit more interesting because 

325
00:15:49,019 --> 00:15:52,000
the compiler doesn't need to know what kind of computer you're running on. It says, 

326
00:15:52,000 --> 00:15:55,220
"Hey, I'm producing this intermediate language and the intermediate language is 

327
00:15:55,220 --> 00:15:57,139
the same for all computers." 

328
00:15:57,139 --> 00:16:00,379
The only thing that has to be different on your computer is you need to have 

329
00:16:00,379 --> 00:16:02,480
this little thing called the JVM 

330
00:16:02,480 --> 00:16:05,509
that knows how to translate this intermediate language 

331
00:16:05,509 --> 00:16:09,298
into what's going on on your computer. So if you have a JVM for your Mac 

332
00:16:09,298 --> 00:16:12,720
or a JVM for your PC or a JVM for your Linux machine, 

333
00:16:12,720 --> 00:16:17,110
they can all run this same low-level intermediate code and do the right thing 

334
00:16:17,110 --> 00:16:18,990
on those computers. Okay, 

335
00:16:18,990 --> 00:16:21,830
and so remember when you set up Eclipse or if you haven't set up Eclipse yet, 

336
00:16:21,830 --> 00:16:25,540
you'll get there soon enough, but when you're wetting up Eclipse, we asked you to 

337
00:16:25,539 --> 00:16:28,389
download and install something called the Java run-time environment and how many 

338
00:16:28,389 --> 00:16:31,620
people remember that? Raise your hand if you remember that? You folks 

339
00:16:31,620 --> 00:16:34,089
guess what the Java runtime environment provided? 

340
00:16:34,089 --> 00:16:37,350
It provided this thing for your computer, okay. 

341
00:16:37,350 --> 00:16:39,459
So you write the program once; 

342
00:16:39,458 --> 00:16:44,149
you compile it once and now that class information that you have, that class file 

343
00:16:44,149 --> 00:16:47,619
can be run on any computer that has this Java Virtual Machine and Java Virtual 

344
00:16:47,619 --> 00:16:51,480
Machines are sort of ubiquitous. They exist for a lot of different computing platforms, okay. 

345
00:16:51,480 --> 00:16:53,879
So that's why they actually do it that way, and it's kind of funky, but it's a 

346
00:16:53,879 --> 00:16:55,549
little bit different. 

347
00:16:55,549 --> 00:16:56,649
Now, 

348
00:16:56,649 --> 00:16:59,590
with that kind of said, that's the low-level stuff. That's kind of what's happening at 

349
00:16:59,590 --> 00:17:02,600
the low level and you don't really need to know that low level intimately. I just 

350
00:17:02,600 --> 00:17:05,500
want you to understand what's happening from the programs you write 

351
00:17:05,500 --> 00:17:08,339
to what happens when they get executed on the computer. 

352
00:17:08,339 --> 00:17:14,079
Now what you do need to know, is how do we begin to write programs in Java. 

353
00:17:14,079 --> 00:17:15,418
In Java, 

354
00:17:15,419 --> 00:17:17,870
you'll see some examples of it today, 

355
00:17:17,869 --> 00:17:21,119
is what we refer to as an object-oriented language, 

356
00:17:21,119 --> 00:17:24,899
okay. So Java is object 

357
00:17:24,900 --> 00:17:25,528
oriented 

358
00:17:25,528 --> 00:17:29,169
and not all languages are object oriented. What is this whole object oriented 

359
00:17:29,169 --> 00:17:32,379
thing about, so you should know what this whole notion is about before you 

360
00:17:32,378 --> 00:17:35,789
start programming in the language that's kind of seeped in the idea. 

361
00:17:35,789 --> 00:17:37,200
The idea 

362
00:17:37,200 --> 00:17:40,680
basically is that a program is written as a bunch of classes, right, so if you 

363
00:17:40,680 --> 00:17:44,630
think about, let's back up for a second, if you think about Karel, right. 

364
00:17:44,630 --> 00:17:47,980
When you are writing Karel programs, of you saw Karel programs, 

365
00:17:47,980 --> 00:17:51,360
you would actually create some Karel program by saying, 

366
00:17:51,359 --> 00:17:52,859
"Public, 

367
00:17:52,859 --> 00:17:54,129
class 

368
00:17:54,130 --> 00:17:56,250
Karel program 

369
00:17:56,250 --> 00:17:57,690
extends 

370
00:17:57,690 --> 00:18:01,100
Super Karel." Let's just say we are Karel model. 

371
00:18:01,099 --> 00:18:05,529
And then you put some stuff in here and you have like your run method in here, maybe 

372
00:18:05,529 --> 00:18:06,519
some other methods 

373
00:18:06,519 --> 00:18:09,519
and what you did was you were creating a class 

374
00:18:09,519 --> 00:18:13,118
that was basically the information for your program, what instructions you 

375
00:18:13,118 --> 00:18:16,599
were actually going to execute as part of that program. So 

376
00:18:16,599 --> 00:18:22,019
what a Java program is is just a set of classes. You may have more than one 

377
00:18:22,019 --> 00:18:25,319
class. Like in Karel right now you always just have one class and inside that 

378
00:18:25,319 --> 00:18:26,898
class you may have a bunch of different methods, but 

379
00:18:26,898 --> 00:18:31,359
you always have one class. A Java program can actually have multiple classes associated 

380
00:18:31,359 --> 00:18:33,788
with it. And when we start in this class, we'll start with some simple ones that are all 

381
00:18:33,788 --> 00:18:34,960
just one class. 

382
00:18:34,960 --> 00:18:36,299
What you have to think about is 

383
00:18:36,299 --> 00:18:39,539
that you can have more than one class, okay? 

384
00:18:39,539 --> 00:18:41,288
And what these classes are, 

385
00:18:41,288 --> 00:18:44,079
what you can think of a class as, 

386
00:18:44,079 --> 00:18:44,769
okay, 

387
00:18:44,769 --> 00:18:46,400
a class 

388
00:18:46,400 --> 00:18:50,970
is just basically an encapsulation 

389
00:18:50,970 --> 00:18:55,839
of some behavior that the program does, just like in Karel's 

390
00:18:55,839 --> 00:18:59,789
world, you had some behavior of a bunch of different methods you define for Karel to 

391
00:18:59,789 --> 00:19:01,430
actually to be able to execute, right, 

392
00:19:01,430 --> 00:19:02,788
those are just different behaviors. 

393
00:19:02,788 --> 00:19:06,858
But you also have some data, so it's behavior and data, 

394
00:19:06,858 --> 00:19:10,470
because in the Java world you are now actually gonna keep around a track of information 

395
00:19:10,470 --> 00:19:13,650
that are not just beepers in some world, but they're actually just 

396
00:19:13,650 --> 00:19:16,380
numbers that you're actually gonna store somewhere and that's your data. 

397
00:19:16,380 --> 00:19:19,930
And so what we do is we think of having the behaviors, all the kind of 

398
00:19:19,930 --> 00:19:21,840
manipulations you might want to do with data, 

399
00:19:21,839 --> 00:19:22,879
along with the data 

400
00:19:22,880 --> 00:19:25,929
and put that all into this thing called the class. 

401
00:19:25,929 --> 00:19:28,690
So just like in Karel where you had a class an you had behaviors, you can just 

402
00:19:28,690 --> 00:19:31,538
imagine, yeah, we're gonna have some behaviors, which means in Java we're gonna 

403
00:19:31,538 --> 00:19:34,319
have some class and define a bunch of methods in that class, 

404
00:19:34,319 --> 00:19:36,918
but we're also gonna have some data associated with it and that whole think 

405
00:19:36,919 --> 00:19:38,929
together is gonna be a class. 

406
00:19:38,929 --> 00:19:41,940
Now, it turns out, the thing that's interesting about classes. Is there any questions 

407
00:19:41,940 --> 00:19:45,870
about the notion of a class? It's just kind of this abstract concept right now. 

408
00:19:45,869 --> 00:19:49,229
The thing that makes classes really powerful is the classes actually get 

409
00:19:49,230 --> 00:19:50,529
organized into hierarchies, 

410
00:19:50,529 --> 00:19:51,450
I mean, just 

411
00:19:51,450 --> 00:19:52,960
draw it here, 

412
00:19:52,960 --> 00:19:53,779
okay. 

413
00:19:53,779 --> 00:19:57,660
And you've actually already seen this in a very small way with Karel, so all the 

414
00:19:57,660 --> 00:20:00,390
things that you've seen in Karel are gonna translate over. 

415
00:20:00,390 --> 00:20:03,600
Remember we talked about the basic Karel model and when you are writing a 

416
00:20:03,599 --> 00:20:06,939
program you could say extends Karel and when you did the basic Karel model, 

417
00:20:06,940 --> 00:20:07,910
you got like 

418
00:20:07,910 --> 00:20:09,540
move and turn left 

419
00:20:09,539 --> 00:20:12,308
and pick beeper and put beeper and that's all you got. 

420
00:20:12,308 --> 00:20:14,889
And then we said, "Hey, you really want to turn right and turn 

421
00:20:14,890 --> 00:20:20,059
around, well there's this thing called Super Karel and Super Karel is just a souped 

422
00:20:20,058 --> 00:20:22,028
up version of Karel." 

423
00:20:22,028 --> 00:20:25,490
Well, guess what, Karel was just a class, 

424
00:20:25,490 --> 00:20:31,108
and Super Karel was also a class, but Super Karel is a class that extends 

425
00:20:31,108 --> 00:20:34,029
the functionality of the basic Karel class, okay. 

426
00:20:34,029 --> 00:20:37,119
So we say that Super Karel, the way we would draw things, 

427
00:20:37,119 --> 00:20:39,859
if we were gonna put boxes around them and draw like the book 

428
00:20:39,859 --> 00:20:42,788
is say that Super Karel is a sub class 

429
00:20:42,788 --> 00:20:46,970
of Karel and Karel is the super class, this is where it's gonna get confusing, but 

430
00:20:46,970 --> 00:20:50,400
super class are the things in some sense that are more general 

431
00:20:50,400 --> 00:20:51,739
and the sub class 

432
00:20:51,739 --> 00:20:56,149
are the things that take the basic idea of some class and extend it. So Super 

433
00:20:56,148 --> 00:20:57,949
Karel does everything that Karel does, 

434
00:20:57,950 --> 00:20:59,319
but it also does 

435
00:20:59,319 --> 00:21:02,918
turn right and turn around, okay. So 

436
00:21:02,919 --> 00:21:07,890
Super Karel is a sub class of Karel or alternatively Karel is a super class 

437
00:21:07,890 --> 00:21:11,230
of Super Karel, which sounds a little bit backward, but the super here and the 

438
00:21:11,230 --> 00:21:15,048
super here mean two different things. Super here means sort of above, 

439
00:21:15,048 --> 00:21:18,980
and super here means cooler than, okay. So don't want to think of them as they mean 

440
00:21:18,980 --> 00:21:22,240
the same thing, it's just an overloaded term, all right? 

441
00:21:22,240 --> 00:21:25,630
So you might say, "Okay, Marion, this is getting a whole little abstract for me." Well, 

442
00:21:25,630 --> 00:21:28,040
let me put it in terms that you understand. 

443
00:21:28,039 --> 00:21:30,549
You're a human being, right? 

444
00:21:30,549 --> 00:21:34,359
At this point, you should say right. And if you're not, come talk to me. All right, 

445
00:21:34,359 --> 00:21:38,229
it wouldn't be the first time. 

446
00:21:38,230 --> 00:21:43,079
So we have humans, okay. Humans are just a class, okay, 

447
00:21:43,079 --> 00:21:46,480
and all humans are 

448
00:21:46,480 --> 00:21:47,640
primates. 

449
00:21:47,640 --> 00:21:50,759
Primates are a super 

450
00:21:50,759 --> 00:21:54,769
class of humans, because all humans are primates, 

451
00:21:54,769 --> 00:21:59,650
all primates are mammals, 

452
00:21:59,650 --> 00:22:01,840
and all mammals are animals. 

453
00:22:01,839 --> 00:22:06,639
So there's actually a much deeper and richer hierarchy say in biology then 

454
00:22:06,640 --> 00:22:08,259
there is with Karel 

455
00:22:08,259 --> 00:22:12,099
and when you actually see Java, Java will eventually have sort of a richer hierarchy 

456
00:22:12,099 --> 00:22:12,939
associated with it. 

457
00:22:12,940 --> 00:22:15,299
Now, the interesting thing about this, this is 

458
00:22:15,299 --> 00:22:21,919
not only humans primates, but monkeys are also primates, okay. 

459
00:22:21,920 --> 00:22:24,950
Humans are not monkeys and monkeys are not humans, so there's not a strict you 

460
00:22:24,950 --> 00:22:27,269
might say, "Well, we don't know about that." But there isn't 

461
00:22:27,269 --> 00:22:30,319
a strict relationship between humans and monkeys other than they're 

462
00:22:30,319 --> 00:22:31,408
both primates, 

463
00:22:31,409 --> 00:22:34,080
and that makes them mammals, and that makes them animals, 

464
00:22:34,079 --> 00:22:36,529
and the whole notion of having this hierarchy 

465
00:22:36,529 --> 00:22:40,490
of classes, right, so you could think of being animal as just a class and it has some 

466
00:22:40,490 --> 00:22:42,058
behaviors. What does it mean to be an animal? 

467
00:22:42,058 --> 00:22:45,700
Well, to be an animal means you digest food, right, 

468
00:22:45,700 --> 00:22:49,039
it's not something like something like [Inaudible] actually, and one of the technical terms I'm 

469
00:22:49,039 --> 00:22:52,509
not a biologist, but just what my friends tell me, embryos pass 

470
00:22:52,509 --> 00:22:53,679
through the 

471
00:22:53,679 --> 00:22:56,540
blastula stage. Any biologists in here? 

472
00:22:56,539 --> 00:22:57,869
Is that right? Yeah. 

473
00:22:57,869 --> 00:23:01,259
Okay, good, good because I was like asking a friend of mine, like, "What differentiates animals 

474
00:23:01,259 --> 00:23:04,369
form plants," and he was like, "Oh, of course, the embryo was passed through the blastula stage and I was 

475
00:23:04,369 --> 00:23:05,048
like, 

476
00:23:05,048 --> 00:23:06,589


477
00:23:06,589 --> 00:23:10,049
"Oh, right on." I had no idea, and I was like, "How do you spell blastula?" 

478
00:23:10,049 --> 00:23:14,480
So I'll just put blastula down here, right. 

479
00:23:14,480 --> 00:23:18,220
So that means, guess what, all mammals 

480
00:23:18,220 --> 00:23:20,239
inherit those same properties. 

481
00:23:20,239 --> 00:23:23,440
Mammals also have some internal digestion of food and also pass 

482
00:23:23,440 --> 00:23:24,840
through this blastula stage, 

483
00:23:24,839 --> 00:23:30,009
but mammals additionally we know are warm blooded 

484
00:23:30,009 --> 00:23:33,960
in general and they have mammary glands which is where the 

485
00:23:33,960 --> 00:23:38,329
name mammal comes from. So mammary glands or just kind of a 

486
00:23:38,329 --> 00:23:40,589
generalization of sweat glands, 

487
00:23:40,589 --> 00:23:44,199
but that's what mammals have, and then all primates are mammals, which means all 

488
00:23:44,200 --> 00:23:45,410
primates 

489
00:23:45,410 --> 00:23:49,149
have all of these same properties plus they have more and so primates 

490
00:23:49,148 --> 00:23:52,548
interestingly enough have five fingers. I didn't know all primates have all five fingers, but evidently 

491
00:23:52,548 --> 00:23:53,848
I'm told that they do. 

492
00:23:53,848 --> 00:23:57,589
They have opposable thumbs. 

493
00:23:57,589 --> 00:24:00,709
And they also have fingernails, but fingernails we just won't put up there. It's 

494
00:24:00,710 --> 00:24:02,390
not a big deal, okay? 

495
00:24:02,390 --> 00:24:05,720
And then we get down to humans and monkey, right, and humans it turns out in 

496
00:24:05,720 --> 00:24:09,460
theory anyway were supposed to have highly developed brains. 

497
00:24:09,460 --> 00:24:11,710
I'll just put 

498
00:24:11,710 --> 00:24:15,829
brains in quotes here because other animals have brains, too, but we're supposed to have highly developed 

499
00:24:15,829 --> 00:24:16,228
brains 

500
00:24:16,229 --> 00:24:21,730
and we have an erect body carriage. 

501
00:24:21,730 --> 00:24:24,679
That's just what we are. We're wrecked brains. 

502
00:24:24,679 --> 00:24:28,240
And monkeys have mother things that are going on, so evidently their brains are 

503
00:24:28,240 --> 00:24:31,140
not as highly developed and they're sort of like their knuckles drag on the 

504
00:24:31,140 --> 00:24:34,370
ground. Sometimes I do that in the morning, but that's not important. 

505
00:24:34,369 --> 00:24:38,449
But that's the whole point. This is the class hierarchy. These are all 

506
00:24:38,450 --> 00:24:42,950
classes and things that are sub classes of some other class means they inherit 

507
00:24:42,950 --> 00:24:45,650
all of the behaviors of the things above them, 

508
00:24:45,650 --> 00:24:47,180
all the way up the chain 

509
00:24:47,180 --> 00:24:50,539
plus they may have their own additional behaviors and that's the key concept here 

510
00:24:50,539 --> 00:24:53,128
of organizing things in classes and you'll see that 

511
00:24:53,128 --> 00:24:56,648
in more specific instance when you get into Java. You saw it already with Karel in 

512
00:24:56,648 --> 00:25:00,449
just really simple example, right. There was four commands for Karel. Super Karel gave 

513
00:25:00,450 --> 00:25:04,940
you those four plus an additional two; that was it; okay? Now, 

514
00:25:04,940 --> 00:25:08,980
besides this idea, there's another key idea that comes up besides this notion of 

515
00:25:08,980 --> 00:25:09,568
classes, 

516
00:25:09,568 --> 00:25:14,230
okay? And that's the notion of the instance of a class, okay. 

517
00:25:14,230 --> 00:25:17,640
And what the instance of a class is, is 

518
00:25:17,640 --> 00:25:22,559
humans are a class. There is no one person that is, "Oh, you are humanity, right?" 

519
00:25:22,558 --> 00:25:24,168
You are a person, right, so [Inaudible] 

520
00:25:24,169 --> 00:25:28,090
what's your name? Eduardo. Huh? Eduardo. 

521
00:25:28,089 --> 00:25:29,569
Eduardo, all right. 

522
00:25:29,569 --> 00:25:32,210
So I hope I'm spelling this right, 

523
00:25:32,210 --> 00:25:34,200
Eduardo; is that right? 

524
00:25:34,200 --> 00:25:38,009
Is an instance of human, I would hope, right. So 

525
00:25:38,009 --> 00:25:39,690
what that means is 

526
00:25:39,690 --> 00:25:43,720
you're going to have things in your Java programs that you create 

527
00:25:43,720 --> 00:25:49,058
which are objects and what an object is to differentiate it from a class, so 

528
00:25:49,058 --> 00:25:50,660
Eduardo is an object. 

529
00:25:50,660 --> 00:25:52,500
I'm sorry; sorry to break it to you. That's 

530
00:25:52,500 --> 00:25:53,380
just 

531
00:25:53,380 --> 00:25:55,440
you're an object. 

532
00:25:55,440 --> 00:26:00,440
An object is an instance of a class; it is a particular example of a class. There 

533
00:26:00,440 --> 00:26:05,179
will be multiple objects or multiple instances potentially of some class, 

534
00:26:05,179 --> 00:26:09,249
and that instance of a class has all of the characteristics of the class 

535
00:26:09,249 --> 00:26:12,630
and all of the other classes above it in the class hierarchy. 

536
00:26:12,630 --> 00:26:16,850
So by looking at this, I could say, "Hey, Eduardo, guess what, you went through the blastula 

537
00:26:16,849 --> 00:26:20,519
phase when you were an embryo." Good times; because you're an animal, right and I know that 

538
00:26:20,519 --> 00:26:22,970
and this is inherited all the way up. 

539
00:26:22,970 --> 00:26:26,190
So that's the important thing to keep in mind is you're going to be writing 

540
00:26:26,190 --> 00:26:29,298
classes; you're going to be writing things that define some set of behavior 

541
00:26:29,298 --> 00:26:36,190
and along with that, you'll be creating instances so that this is an instance of the class 

542
00:26:36,190 --> 00:26:40,230
and the instances are what we refer to as objects so all of your instances in 

543
00:26:40,230 --> 00:26:43,440
the world are just things that we think of as objects and your classes are in 

544
00:26:43,440 --> 00:26:44,219
some sense 

545
00:26:44,219 --> 00:26:46,269
the templates 

546
00:26:46,269 --> 00:26:49,230
for those objects, okay. 

547
00:26:49,230 --> 00:26:51,680
So any questions about the general concepts; I know they're a little bit 

548
00:26:51,680 --> 00:26:56,200
high level, but it's important for you to kind of understand. Okay. 

549
00:26:56,200 --> 00:26:57,610
So with that said, 

550
00:26:57,609 --> 00:26:59,558
let's actually 

551
00:26:59,558 --> 00:27:00,769
begin to look at 

552
00:27:00,769 --> 00:27:03,629
this notion in Java, okay? 

553
00:27:03,630 --> 00:27:10,630
And so the way that this is gonna work uh-huh? [Inaudible] in Karel, what was the object? 

554
00:27:10,990 --> 00:27:16,079
So in Karel, it turned out what you're actually just creating was 

555
00:27:16,079 --> 00:27:20,548
a single Karel object was being created that contained your program 

556
00:27:20,548 --> 00:27:22,170
and that's what was actually run. 

557
00:27:22,170 --> 00:27:26,230
So you created the class Karel, and when that puppy actually sort of fired up and 

558
00:27:26,230 --> 00:27:28,298
you saw little Karel running around in the world, 

559
00:27:28,298 --> 00:27:31,470
that was a Karel object; that was an instance of your class. 

560
00:27:31,470 --> 00:27:34,779
Now, you actually didn't see multiple objects or multiple instances there. 

561
00:27:34,779 --> 00:27:37,720
There was only one Karel instance. So there it's very it's a good question because it's 

562
00:27:37,720 --> 00:27:40,319
easy to get confused between the instance 

563
00:27:40,319 --> 00:27:42,569
and the class in that case because it was only one. 

564
00:27:42,569 --> 00:27:46,220
But in here you'll actually see we'll actually create classes and we'll have multiple instances of 

565
00:27:46,220 --> 00:27:53,220
them, which are running Karel with basically the instance of that object. Okay, question? 

566
00:27:55,529 --> 00:27:59,579
So, basically like you can have, like several 

567
00:27:59,579 --> 00:28:00,319
Karels 

568
00:28:00,319 --> 00:28:02,819
running around in like one program? 

569
00:28:02,819 --> 00:28:06,458
You could if we sort of set it up that way. In the Karel, 

570
00:28:06,459 --> 00:28:09,440
the way it's kind of set up is it only allows you, it only sort of behind 

571
00:28:09,440 --> 00:28:12,169
the scenes creates for you this one instance of Karel, 

572
00:28:12,169 --> 00:28:15,989
but in some, you know, alternative Karel universe, we could have actually have just taken her 

573
00:28:15,989 --> 00:28:16,730
class and said, 

574
00:28:16,730 --> 00:28:19,849
"Hey, guess what, we're gonna just create multiple Karel instances from 

575
00:28:19,849 --> 00:28:23,159
your class and have them all run around in the same room." We could have, 

576
00:28:23,160 --> 00:28:24,199
and guess what, 

577
00:28:24,199 --> 00:28:26,798
that's what seemed to have happened in this room, right. Somewhere along the way, there 

578
00:28:26,798 --> 00:28:28,119
was this class human 

579
00:28:28,119 --> 00:28:31,559
and someone came along and created multiple instances of you. Well, I wouldn't 

580
00:28:31,559 --> 00:28:32,599
just say just one person, 

581
00:28:32,599 --> 00:28:34,649
but now there's multiple instances of you, 

582
00:28:34,650 --> 00:28:37,030
right, and you're all running around in the world doing your thing and you interact 

583
00:28:37,029 --> 00:28:39,599
with each other and guess what 

584
00:28:39,599 --> 00:28:43,519
objects actually do; they interact with each other, okay? 

585
00:28:43,519 --> 00:28:45,089
So with that said, 

586
00:28:45,089 --> 00:28:47,558
there is gonna be some functionality we're gonna use that was written by 

587
00:28:47,558 --> 00:28:50,548
someone else. So just like Karel, the basic version of Karel was written by 

588
00:28:50,548 --> 00:28:53,500
someone else. When we start with Java, we're gonna start with some set of 

589
00:28:53,500 --> 00:28:56,069
scaffolding or libraries that were written by someone else 

590
00:28:56,069 --> 00:29:01,139
that are gonna allow us to do a bunch of powerful things in Java very early on, okay? 

591
00:29:01,140 --> 00:29:04,900
And this is something that is called the ACM program hierarchy. So it sounds 

592
00:29:04,900 --> 00:29:06,250
all complicated. 

593
00:29:06,250 --> 00:29:09,609
But all this is, right, and much the same way that I drew that picture over there 

594
00:29:09,609 --> 00:29:12,659
with animals, mammals, primates, humans and monkeys, 

595
00:29:12,660 --> 00:29:14,090
this is a hierarchy 

596
00:29:14,089 --> 00:29:19,319
of classes that exist in Java's world or at least are provided by the ACM and you 

597
00:29:19,319 --> 00:29:22,970
might say, "Who is the ACM?" Anybody know who the ACM is? 

598
00:29:22,970 --> 00:29:25,870
They're big; they're bad; they're nationwide. 

599
00:29:25,869 --> 00:29:28,000
They're the Association for Computing Machinery. 

600
00:29:28,000 --> 00:29:29,788
It's the oldest computing society. 

601
00:29:29,788 --> 00:29:32,720
They've been around for actually for about 60 years or so. And you're like, 

602
00:29:32,720 --> 00:29:34,819
"But Marion, I thought you said 100 years. 

603
00:29:34,819 --> 00:29:37,409
Yeah, before then, people called it math. 

604
00:29:37,410 --> 00:29:39,900
So Association for 

605
00:29:39,900 --> 00:29:42,190
Computing Machinery has this program hierarchy 

606
00:29:42,190 --> 00:29:45,869
and what that means is the kind of programs that we write in this class, 

607
00:29:45,868 --> 00:29:48,928
just like when you wrote your Karel programs you extend Karel or you 

608
00:29:48,929 --> 00:29:50,419
extend Super Karel, 

609
00:29:50,419 --> 00:29:53,929
you're going to be extending different kinds of programs, either a console 

610
00:29:53,929 --> 00:29:56,420
program which is something that produces textural output, 

611
00:29:56,420 --> 00:29:59,880
a dialog program which brings up little dialogue boxes that ask for 

612
00:29:59,880 --> 00:30:00,740
information 

613
00:30:00,740 --> 00:30:04,839
or a graphics program that actually draws some pretty funky stuff on the screen. 

614
00:30:04,839 --> 00:30:07,769
All of those classes are 

615
00:30:07,769 --> 00:30:12,679
classes that are inheriting from a class, a super class called program. 

616
00:30:12,679 --> 00:30:15,890
So all of the things that you write as a dialogue program or a graphics program 

617
00:30:15,890 --> 00:30:18,070
are all something that are programs. 

618
00:30:18,069 --> 00:30:21,928
And all programs are something uptight J-Applet, which just means Java 

619
00:30:21,929 --> 00:30:22,530
Applet 

620
00:30:22,529 --> 00:30:26,210
and all Java Applets, are of some type called Applet. Anyone ever heard of 

621
00:30:26,210 --> 00:30:27,940
an Applet? 

622
00:30:27,940 --> 00:30:31,120
An Applet is something you can run on your web page, interestingly 

623
00:30:31,119 --> 00:30:32,119
enough. That's 

624
00:30:32,119 --> 00:30:35,379
kind of where the term comes from. It's like a lightweight application, and 

625
00:30:35,380 --> 00:30:37,700
applet application, but small. 

626
00:30:37,700 --> 00:30:41,220
And so it turns out since all of the programs that you're writing are actually 

627
00:30:41,220 --> 00:30:43,309
inherit the properties of being an applet, 

628
00:30:43,309 --> 00:30:46,779
they actually will be applets, which means you can put them on your web page and 

629
00:30:46,779 --> 00:30:50,160
run your programs on your web page if you want and later on in the class we'll talk about how to do 

630
00:30:50,160 --> 00:30:52,120
that, 

631
00:30:52,119 --> 00:30:55,279
okay? But in this class, as least, you're not gonna write anything that 

632
00:30:55,279 --> 00:30:59,180
directly extends like J-Applet or Applet or program. Everything you write is 

633
00:30:59,180 --> 00:31:00,560
gonna extend down to this level, 

634
00:31:00,559 --> 00:31:03,419
but it's important to know that there's different kinds of programs that you can actually 

635
00:31:03,420 --> 00:31:05,600
write at that level. So 

636
00:31:05,599 --> 00:31:09,849
let's look at an example of a Java program, and I'll show you your first Java 

637
00:31:09,849 --> 00:31:10,699
program today. 

638
00:31:10,700 --> 00:31:16,100
So we can feel good about Java no it's not that one. 

639
00:31:16,099 --> 00:31:17,230
It's this one. 

640
00:31:17,230 --> 00:31:20,529
It's small; it's tiny; it's fun; it's Java. All right, 

641
00:31:20,529 --> 00:31:23,619
so let me expand this whole thing out 

642
00:31:23,619 --> 00:31:27,469
so you can see the whole program still fits on one screen, okay. 

643
00:31:27,470 --> 00:31:30,690
And you might suddenly notice there's a bunch of things in this program that look very 

644
00:31:30,690 --> 00:31:32,350
similar to Karel. 

645
00:31:32,349 --> 00:31:34,568
That's because Karel was implemented in Java. 

646
00:31:34,568 --> 00:31:38,190
So the first thing you want to look at here is we have a file called helloprogram.java, 

647
00:31:38,190 --> 00:31:41,759
just like your Karel programs are written with a .Java file, 

648
00:31:41,759 --> 00:31:43,750
you are creating a .java file here. 

649
00:31:43,750 --> 00:31:46,849
This is a source file because it has source code in it. 

650
00:31:46,849 --> 00:31:50,969
Up at the top, you have a comment, "Gee, it actually uses the exactly same structure as Karel 

651
00:31:50,970 --> 00:31:54,009
comments." Yeah, because Karel comments were actually Java comments. Comments in Karel and 

652
00:31:54,009 --> 00:31:55,960
Java are exactly the same. 

653
00:31:55,960 --> 00:31:59,829
Just like you imported stanford.karel.star, now you're gonna be 

654
00:31:59,829 --> 00:32:03,309
using the stuff that the lovely folks at the ACM have provided for you, so you're 

655
00:32:03,309 --> 00:32:08,970
going to import acm.graphics.star and acm.program.star. What 

656
00:32:08,970 --> 00:32:10,150
are these things? 

657
00:32:10,150 --> 00:32:11,120
These are just 

658
00:32:11,119 --> 00:32:14,428
well, I won't back up because we're not on the slide. 

659
00:32:14,429 --> 00:32:17,509
These are just remember I said you write your classes and someone else may have 

660
00:32:17,509 --> 00:32:20,970
written some classes and they all get linked together before they're executed. 

661
00:32:20,970 --> 00:32:23,808
These are just some other classes that someone else wrote that are going to get 

662
00:32:23,808 --> 00:32:25,119
linked into what you do. 

663
00:32:25,119 --> 00:32:28,699
Right, they provide you the definition for things like what a graphics program 

664
00:32:28,700 --> 00:32:29,970
actually is. 

665
00:32:29,970 --> 00:32:33,600
So now, what you're gonna do, as we talked about, all Java programs are just 

666
00:32:33,599 --> 00:32:35,308
the collection of classes, 

667
00:32:35,308 --> 00:32:38,428
so just like in Karel, we have public class 

668
00:32:38,429 --> 00:32:40,250
and some name for your program. 

669
00:32:40,250 --> 00:32:44,150
Here we'll call it Hello program. And a Hello program is a particular kind of 

670
00:32:44,150 --> 00:32:47,970
program. It doesn't extend Super Karel because it's not a Super Karel program anymore. 

671
00:32:47,970 --> 00:32:51,450
It's gonna be a graphics program. It's actually gonna draw some stuff on the screen, 

672
00:32:51,450 --> 00:32:53,788
so it's gonna extend the graphics program. 

673
00:32:53,788 --> 00:32:57,230
But all the boilerplates should look the same, right, that's what we had you do 

674
00:32:57,230 --> 00:33:00,849
Karel because all the stuff from Karel just translates directly over to Java, 

675
00:33:00,849 --> 00:33:04,529
except now we're sort of cooking with gas; now we're doing the real thing, okay. 

676
00:33:04,529 --> 00:33:08,779
So it extends graphics program and guess what, inside here we have a run method 

677
00:33:08,779 --> 00:33:12,259
just like Karel and that's where the program begins executing. 

678
00:33:12,259 --> 00:33:16,390
Now, where things get funky is you're like, "Oh, may what happened to pick 

679
00:33:16,390 --> 00:33:20,278
beeper and plug beeper and like life was so good; it was easy and you know, turn right and it was like 

680
00:33:20,278 --> 00:33:21,589
the extent of it. 

681
00:33:21,589 --> 00:33:26,000
What is it like add nugi label, hello world, like what is this all about, okay?" 

682
00:33:26,000 --> 00:33:27,609
We'll go through this step by step. 

683
00:33:27,609 --> 00:33:30,368
All this is saying is when you create a graphics program, we'll go through the 

684
00:33:30,368 --> 00:33:31,730
details in just a second, 

685
00:33:31,730 --> 00:33:35,230
you're gonna get a blank screen, you're going to get an empty canvas in some sense. You're gonna be 

686
00:33:35,230 --> 00:33:37,870
an artist and you're gonna draw stuff on that canvas, and the thing that you're gonna draw stuff on that canvas 

687
00:33:37,869 --> 00:33:41,319
and the thing that you're gonna draw on that canvas is some label and all 

688
00:33:41,319 --> 00:33:44,849
that label is is just basically words and the words are gonna be Hello 

689
00:33:44,849 --> 00:33:47,519
World, because you wanna write Hello World on the screen and you wanna 

690
00:33:47,519 --> 00:33:49,819
write it at a particular location on the screen. 

691
00:33:49,819 --> 00:33:52,939
The location on the screen you wanna write it at is 

692
00:33:52,940 --> 00:33:56,070
100,75 and I'll tell you where that is on the screen in just a second. 

693
00:33:56,069 --> 00:33:59,269
And then once you create this little label, you're gonna add it to your 

694
00:33:59,269 --> 00:34:01,700
canvas. You're gonna say, "I have some canvas, 

695
00:34:01,700 --> 00:34:04,370
plop that puppy onto my canvas," okay? 

696
00:34:04,369 --> 00:34:07,969
So let's run the program and I'll just plop it onto the canvas or you'll see 

697
00:34:07,970 --> 00:34:10,188
what's going on. Life will be good. 

698
00:34:10,188 --> 00:34:15,489
So we run this program, we drop the microphone. Dropped the microphone again, 

699
00:34:15,489 --> 00:34:21,588
all 

700
00:34:21,588 --> 00:34:27,409
right. 

701
00:34:27,409 --> 00:34:31,509
So we want to do Hello program. 

702
00:34:31,509 --> 00:34:35,028
We're getting excited. We're running; we're running. 

703
00:34:35,028 --> 00:34:38,559
The disc is just turning away and there's your first Java program. You're 

704
00:34:38,559 --> 00:34:40,769
all Java programmers now. 

705
00:34:40,768 --> 00:34:44,818
What did you do; you created a graphics program, which brought up this big window 

706
00:34:44,818 --> 00:34:48,108
and said, "I'm blank canvas. Draw on me." 

707
00:34:48,108 --> 00:34:49,159
And you said, "All right, 

708
00:34:49,159 --> 00:34:51,699
Hello World woohoo 

709
00:34:51,699 --> 00:34:54,469
and I'm done," because that's all you did. You said here's Hello World, put it 

710
00:34:54,469 --> 00:34:55,749
up on the canvas for me 

711
00:34:55,748 --> 00:34:58,908
at a location 100,75 and thanks for playing; that's all I'm gonna 

712
00:34:58,909 --> 00:35:00,130
do. But 

713
00:35:00,130 --> 00:35:03,430
now you've actually gone through the whole process of compiling your Java 

714
00:35:03,429 --> 00:35:06,489
program and turning it into this intermediate code and this intermediate code gets 

715
00:35:06,489 --> 00:35:07,099
executed and 

716
00:35:07,099 --> 00:35:09,779
you actually did something and that's like half the battle right there. 

717
00:35:09,780 --> 00:35:12,750
The next nine weeks is the other half of the battle, but half the battle is 

718
00:35:12,750 --> 00:35:16,579
getting this up. I kid you not, really. If you can make that happen, 

719
00:35:16,579 --> 00:35:17,659
you're just 

720
00:35:17,659 --> 00:35:19,068
most of the way there. 

721
00:35:19,068 --> 00:35:22,248
So let's do something a little more exciting than this. Let's actually do some 

722
00:35:22,248 --> 00:35:24,989
interaction with the user. Let me show you another program. 

723
00:35:24,989 --> 00:35:28,129
Remember this one is a graphics program. I told you there was a bunch of different 

724
00:35:28,130 --> 00:35:30,479
kinds of programs you can have 

725
00:35:30,478 --> 00:35:33,239
when I showed you the picture. I said, "We have a graphics program." Let's look at something 

726
00:35:33,239 --> 00:35:40,048
called the console program over here. Uh-huh. [Inaudible]. No, 

727
00:35:40,048 --> 00:35:41,099
not in Java. 

728
00:35:41,099 --> 00:35:44,009
You're always extending one kind of program and a graphics program will 

729
00:35:44,009 --> 00:35:47,889
actually, as you saw you can put up text. A console program is just meant to be a 

730
00:35:47,889 --> 00:35:50,918
textural program, so you're not gonna do any drawing. 

731
00:35:50,918 --> 00:35:55,048
But here's another program, right, again, a lot of the same things is before. You have 

732
00:35:55,048 --> 00:35:56,599
some comment up at the top. 

733
00:35:56,599 --> 00:35:57,900
You have some 

734
00:35:57,900 --> 00:36:01,019
libraries that you're gonna import. In this case, you're not doing anything with graphics, 

735
00:36:01,018 --> 00:36:04,528
so you don't need to import acm.graphics.star, you just need o 

736
00:36:04,528 --> 00:36:09,268
import acm.program.star which just 

737
00:36:09,268 --> 00:36:11,909
says, "Get me all the standard stuff for a program." If you're doing graphics, you 

738
00:36:11,909 --> 00:36:15,368
also need to have a second line for acm.graphics.star. If you're not 

739
00:36:15,369 --> 00:36:17,209
doing graphics, you don't. 

740
00:36:17,208 --> 00:36:20,908
So again, public class. This one called add-to integers because guess what, it's gonna 

741
00:36:20,909 --> 00:36:24,358
ask the user [Inaudible] programs, put tow integers and add them together, 

742
00:36:24,358 --> 00:36:27,139
but in fact, it's gonna do something interactive with the user which is pretty 

743
00:36:27,139 --> 00:36:28,489
exciting in itself. 

744
00:36:28,489 --> 00:36:31,798
This is gonna extend the console program because it's not gonna have 

745
00:36:31,798 --> 00:36:35,858
any graphics. Aw, yeah I know, it's sad times, but sometimes text is very 

746
00:36:35,858 --> 00:36:36,808
powerful. 

747
00:36:36,809 --> 00:36:38,290
What's it gonna do when it runs? 

748
00:36:38,289 --> 00:36:41,179
It's gonna write out to the screen and this time we're gonna use something 

749
00:36:41,179 --> 00:36:45,389
called print lin, we just like to drop some vowels here and there, which stands for 

750
00:36:45,389 --> 00:36:49,679
print line, and if print a line, this program adds two numbers, then it's gonna 

751
00:36:49,679 --> 00:36:53,379
read an integer from the user and we'll go through all this stuff in more detail. 

752
00:36:53,380 --> 00:36:57,110
Don't worry; this is jus a high-level overview so you get some basic idea of what 

753
00:36:57,110 --> 00:36:58,409
Java looks like. 

754
00:36:58,409 --> 00:37:01,979
It asks the user for N1, right, because you have to be very scientific, so rather 

755
00:37:01,978 --> 00:37:04,598
than give me the first number, you say enter N1, right, and 

756
00:37:04,599 --> 00:37:05,510
suddenly 

757
00:37:05,510 --> 00:37:07,079
we're much more formal. 

758
00:37:07,079 --> 00:37:10,298
Enter N2, right, and so what this is actually doing it's asking the user for a 

759
00:37:10,298 --> 00:37:14,009
number and whatever the number the user gives us, we stick in this location 

760
00:37:14,009 --> 00:37:15,199
called N1. 

761
00:37:15,199 --> 00:37:18,038
And whatever the number the user give us here we're gonna stick in a location 

762
00:37:18,039 --> 00:37:21,079
called N2 and we'll actually talk about what these locations are and how they get set 

763
00:37:21,079 --> 00:37:22,470
up and everything next time, 

764
00:37:22,469 --> 00:37:25,529
but I just want you to see something before we can kind of go into all the details because 

765
00:37:25,530 --> 00:37:27,140
we gotta start somewhere. 

766
00:37:27,139 --> 00:37:30,018
Then we're gonna add N1 and N2 together and store them in a place 

767
00:37:30,018 --> 00:37:31,149
called total 

768
00:37:31,150 --> 00:37:33,460
and then we're gonna write out the total is, 

769
00:37:33,460 --> 00:37:35,030
whatever the total is, and then 

770
00:37:35,030 --> 00:37:39,190
a period. Right, so this is in some sense the world's most expensive calculator that 

771
00:37:39,190 --> 00:37:40,338
adds two numbers. 

772
00:37:40,338 --> 00:37:43,469
And we'll go ahead and run it, 

773
00:37:43,469 --> 00:37:44,139


774
00:37:44,139 --> 00:37:46,189
add two integers. We're 

775
00:37:46,188 --> 00:37:50,058
compiling; we're feeling good 

776
00:37:50,059 --> 00:37:53,920
and that's the program we want to run, 

777
00:37:53,920 --> 00:37:56,670
and now this comes along and notice, 

778
00:37:56,670 --> 00:38:00,259
now we have some window that rather than putting graphics all over it and telling it 

779
00:38:00,259 --> 00:38:04,710
where to display some words like Hello World, we just said, "Write some line," and 

780
00:38:04,710 --> 00:38:07,329
so what it's gonna do is just sequentially write lines on the screen 

781
00:38:07,329 --> 00:38:09,530
because this is what we think of as a console. 

782
00:38:09,530 --> 00:38:13,080
All a console really is, the way you can think about it is it's a window that contains 

783
00:38:13,079 --> 00:38:13,659
texts 

784
00:38:13,659 --> 00:38:17,420
and can potentially interact with the user, so there's places where we might ask the user 

785
00:38:17,420 --> 00:38:17,969
for input. 

786
00:38:17,969 --> 00:38:21,479
So we said if this program adds two numbers, I hope you can see this in the back. It's tiny, 

787
00:38:21,478 --> 00:38:23,009
tiny font. 

788
00:38:23,009 --> 00:38:25,818
Enter N1 and it's sitting there with a blinking cursor, and any time you see the 

789
00:38:25,818 --> 00:38:28,699
blinking cursor, that means, "Hey, I'm expecting some value." 

790
00:38:28,699 --> 00:38:32,168
So give me something of value. What's some integer? [Inaudible]. 

791
00:38:32,168 --> 00:38:35,400
Twelve; someone said 12; someone said one, so I'll take 12 as N1 and 

792
00:38:35,400 --> 00:38:38,460
then it asks for N2. I'll give it one 

793
00:38:38,460 --> 00:38:43,909
and low and behold, it says the total is 13 period, end of program, okay? 

794
00:38:43,909 --> 00:38:46,108
At this point, there's a blinking cursor, but 

795
00:38:46,108 --> 00:38:47,798
the program is done. 

796
00:38:47,798 --> 00:38:52,048
But now you've just seen a real Java program that actually takes in values 

797
00:38:52,048 --> 00:38:53,329
from the user, 

798
00:38:53,329 --> 00:38:56,538
computes some, does some computation on them and displays output, 

799
00:38:56,539 --> 00:39:00,079
okay? And this is a console program as opposed to a graphics program because 

800
00:39:00,079 --> 00:39:02,519
all the stuff we're doing here is textural. Okay, 

801
00:39:02,518 --> 00:39:06,088
so any questions about the basic idea of 

802
00:39:06,088 --> 00:39:09,148
classes or objects or these different programs we're writing? The programs 

803
00:39:09,148 --> 00:39:11,348
that are running, when they run, 

804
00:39:11,349 --> 00:39:12,800
they are being, 

805
00:39:12,800 --> 00:39:16,519
they're objects. They're instances that are being run for you. 

806
00:39:16,518 --> 00:39:20,988
What they're doing as instances, they're objects that are inheriting all the 

807
00:39:20,989 --> 00:39:24,889
behavior from the class template and then when we run, an instance is 

808
00:39:24,889 --> 00:39:31,889
actually created in this run. Uh-huh? [Inaudible]. 

809
00:39:34,478 --> 00:39:37,578
Because if you say acm.star, strangely enough, you won't necessarily 

810
00:39:37,579 --> 00:39:39,379
get everything 

811
00:39:39,378 --> 00:39:42,588
underneath ACM as well. You'll get everything at that level. 

812
00:39:42,588 --> 00:39:46,418
So there's actually a package for ACM and there's a package ACM graphics, and 

813
00:39:46,418 --> 00:39:48,748
there's a package ACM program 

814
00:39:48,748 --> 00:39:53,000
and what you really want is everything inside ACM program and ACM graphics, 

815
00:39:53,000 --> 00:39:56,389
not just the things that are in ACM graphics by itself. Yeah, 

816
00:39:56,389 --> 00:39:58,158
it's an 

817
00:39:58,159 --> 00:39:59,640
interesting 

818
00:39:59,639 --> 00:40:02,038
technical question, and you 

819
00:40:02,039 --> 00:40:09,039
don't need to worry about the details. Just add both of them and you'll be fine. [Inaudible]. No, 

820
00:40:10,108 --> 00:40:12,958
the console program you just print out. That's one of the differences with the 

821
00:40:12,958 --> 00:40:15,169
graphics [Inaudible]. 

822
00:40:15,170 --> 00:40:18,420
With the graphics program, you have to tell it where stuff goes. 

823
00:40:18,420 --> 00:40:25,420
Console program is just writing out line by line. Uh-huh? [Inaudible]. Sorry. [Inaudible]. 

824
00:40:36,088 --> 00:40:38,969
Yeah, every time you run a Karel program, you can think of what it's doing is 

825
00:40:38,969 --> 00:40:42,019
creating an instance of Karel which is that little guy you see on the screen 

826
00:40:42,018 --> 00:40:45,498
and he's going around and doing stuff, so in Karel there was only one instance 

827
00:40:45,498 --> 00:40:47,068
of the object. 

828
00:40:47,068 --> 00:40:50,058
Here you'll actually see we'll create some objects where we can have multiple 

829
00:40:50,059 --> 00:40:53,540
incidents of an object in the same roll and I'll show you some examples of that in just a second, but we 

830
00:40:53,539 --> 00:40:56,298
just haven't gotten there yet, okay? 

831
00:40:56,298 --> 00:40:58,179
So what we're gonna do now, 

832
00:40:58,179 --> 00:41:00,599
is we're gonna think a little bit about 

833
00:41:00,599 --> 00:41:03,778
graphics that we can actually draw. Because the graphics world it's easiest to see 

834
00:41:03,778 --> 00:41:08,768
multiple objects. We're gonna put multiple stuff up inside our little graphics canvas. So 

835
00:41:08,768 --> 00:41:14,798
what's this whole graphics thing about? 

836
00:41:14,798 --> 00:41:17,938
Let me tell you a little bit about the graphics window and then we'll put a 

837
00:41:17,938 --> 00:41:21,598
couple different objects up in the graphics window and you can see what I'm talking 

838
00:41:21,599 --> 00:41:22,528
about. 

839
00:41:22,528 --> 00:41:27,199
So in terms of graphics, all graphics that we're gonna do are modeled called 

840
00:41:27,199 --> 00:41:30,648
a collage model and if you remember in the days of yore when you were a week 

841
00:41:30,648 --> 00:41:31,148
tyke, 

842
00:41:31,148 --> 00:41:34,888
did anyone have like a little felt board with little felt animals that you put on 

843
00:41:34,889 --> 00:41:35,659
it? 

844
00:41:35,659 --> 00:41:38,068
Yeah, that was a collage, 

845
00:41:38,068 --> 00:41:42,088
or if you had a big piece of paper and you had some like crazy, not crazy 

846
00:41:42,088 --> 00:41:44,078
glue, what was that, glue stick. You 

847
00:41:44,079 --> 00:41:45,539
don't smell that stuff too much like, 

848
00:41:45,539 --> 00:41:48,829
but you would take some piece of paper and you're like, "Oh, here's a picture of a cat," and you 

849
00:41:48,829 --> 00:41:51,500
would like put some glue on the back of it and put it up on there, and then 

850
00:41:51,500 --> 00:41:55,500
you'd say, "Oh, here's a picture of a dog," and put it up on there. That's the model 

851
00:41:55,500 --> 00:41:57,000
for graphics in Java. 

852
00:41:57,000 --> 00:41:59,590
We're gonna have these little pictures or little objects and we're 

853
00:41:59,590 --> 00:42:03,380
gonna say, "Show up here and show up over there." So what 

854
00:42:03,380 --> 00:42:04,749
you have is a collage 

855
00:42:04,748 --> 00:42:07,259
which starts off as a blank canvas 

856
00:42:07,259 --> 00:42:11,248
and you're going to put objects onto that canvas, okay? 

857
00:42:11,248 --> 00:42:15,328
And so what we can do is create various kinds of shapes or pieces of texts and 

858
00:42:15,329 --> 00:42:18,699
put them up in various places on the canvas and you just saw an example of that with 

859
00:42:18,699 --> 00:42:19,829
Hello World, 

860
00:42:19,829 --> 00:42:23,148
but I'll show you some of the other things that you can create. 

861
00:42:23,148 --> 00:42:26,298
Two different kinds of objects that exist in the graphics world, 

862
00:42:26,298 --> 00:42:28,829
one you just saw. It's called a GLabel for 

863
00:42:28,829 --> 00:42:30,269
a graphic label. 

864
00:42:30,269 --> 00:42:34,019
This is just text in some sense. It's text that you can put up in the 

865
00:42:34,019 --> 00:42:34,489
world. 

866
00:42:34,489 --> 00:42:38,769
There's also a GRect, which is a rectangle, oddly enough, 

867
00:42:38,769 --> 00:42:42,829
a GOval, which is an oval or if you actually make the height and width the 

868
00:42:42,829 --> 00:42:46,230
same, it becomes a circle, right. So that's why we don't have circle; we have oval 

869
00:42:46,230 --> 00:42:48,639
and same thing with rect versus square because 

870
00:42:48,639 --> 00:42:50,618
all squares are rectangle, 

871
00:42:50,619 --> 00:42:55,449
and GLine, which just means a graphic line. So these are the different kinds of 

872
00:42:55,449 --> 00:42:56,739
objects we can have. 

873
00:42:56,739 --> 00:42:58,670
These are classes. 

874
00:42:58,670 --> 00:43:02,358
They are templates for objects. We are going to create particular instances of these 

875
00:43:02,358 --> 00:43:04,259
objects and put them up in the collage, 

876
00:43:04,260 --> 00:43:08,449
but these just tell us the kinds of things we can have in the general class. So 

877
00:43:08,449 --> 00:43:10,499
if we come back, 

878
00:43:10,498 --> 00:43:11,819
if we close this guy, 

879
00:43:11,820 --> 00:43:14,329
and we come back over here to fund the 

880
00:43:14,329 --> 00:43:15,609
below program, 

881
00:43:15,608 --> 00:43:17,798
what we've done 

882
00:43:17,798 --> 00:43:18,918
is we've said, 

883
00:43:18,918 --> 00:43:21,819
"I want a GLabel. GLabel is the class. 

884
00:43:21,820 --> 00:43:26,789
When I say new GLabel, what that actually does is says, "Give me a new 

885
00:43:26,789 --> 00:43:31,949
instance of that class. Give me an object that is a GLabel," and the things that you're 

886
00:43:31,949 --> 00:43:36,129
going to specify about that particular instance or it has some text associated 

887
00:43:36,130 --> 00:43:36,709
with it, 

888
00:43:36,708 --> 00:43:40,538
which is Hello World. We've put all the texts inside the double quotes, okay. 

889
00:43:40,539 --> 00:43:44,099
So Hello World without the double quotes is actually the text associated with 

890
00:43:44,099 --> 00:43:46,838
this label and we give it some location, 

891
00:43:46,838 --> 00:43:49,998
100,75. So now this little object, 

892
00:43:49,998 --> 00:43:53,509
okay, which is an instance of a label says, "Hey, I'm one particular label in the 

893
00:43:53,509 --> 00:43:53,989
world 

894
00:43:53,989 --> 00:43:58,099
and the kind of label I am, I say Hello World, and I'm at location 

895
00:43:58,099 --> 00:43:58,640


896
00:43:58,639 --> 00:44:01,629
100,75," and 

897
00:44:01,630 --> 00:44:04,269
it's like, "Okay you have this label, what are you gonna do with it." And I'm like, 

898
00:44:04,268 --> 00:44:07,978
"Put it on the canvas," and the way you put it on the canvas is you say, add. 

899
00:44:07,978 --> 00:44:11,169
So all graphics programs, when you say add, 

900
00:44:11,170 --> 00:44:14,420
there is something that you will specify to add, and the things that you were 

901
00:44:14,420 --> 00:44:16,829
specifying to add are instances. 

902
00:44:16,829 --> 00:44:20,309
They are individual objects that you're going to put on the canvas and the way 

903
00:44:20,309 --> 00:44:23,750
you get those individual objects is you create a new version 

904
00:44:23,750 --> 00:44:27,498
of some particular class, okay? So 

905
00:44:27,498 --> 00:44:30,959
this creates that new label, location 175 and 

906
00:44:30,960 --> 00:44:33,659
when it gets added, it gets put up there. Now, 

907
00:44:33,659 --> 00:44:36,858
there is other kinds of things we could do with this, so if we're kind of return over 

908
00:44:36,858 --> 00:44:40,278
here, 

909
00:44:40,278 --> 00:44:44,759
this is just the add-to integers program, let's do add-to integers real quickly 

910
00:44:44,759 --> 00:44:48,579
17, 25, 42, writes up same thing you just saw except now 

911
00:44:48,579 --> 00:44:51,449
in excruciating detail. 

912
00:44:51,449 --> 00:44:55,019
Let's say we want to do something that makes a GLabel more funky than 

913
00:44:55,018 --> 00:44:57,068
we originally had, okay? 

914
00:44:57,068 --> 00:45:00,438
So again, we're gonna have our Hello Program that's gonna extend the 

915
00:45:00,438 --> 00:45:03,518
graphics program. Then we're gonna do things slightly differently. What we're gonna 

916
00:45:03,518 --> 00:45:08,488
do here is we're going to create a new instance of a GLabel object. So if we say 

917
00:45:08,489 --> 00:45:12,179
new GLabel and again, we're gonna name is Hello World and 

918
00:45:12,179 --> 00:45:15,048
100,75, so I have some label that's 

919
00:45:15,048 --> 00:45:18,380
Hello World and location 100,75, and I say, "Hey, you know what label, 

920
00:45:18,380 --> 00:45:21,759
I want you to look different than you actually are, okay? 

921
00:45:21,759 --> 00:45:24,719
So now what do I have this object, I have this little label, you can think of 

922
00:45:24,719 --> 00:45:27,418
it as a little object that sits somewhere in the world that's not being 

923
00:45:27,418 --> 00:45:30,460
displayed yet because I haven't added it yet to my canvas. 

924
00:45:30,460 --> 00:45:33,809
It's being stored somewhere which I have named label, okay, 

925
00:45:33,809 --> 00:45:37,509
and we'll talk about this notion of GLabel, label next time, but it's something I've 

926
00:45:37,509 --> 00:45:38,588
created called Label 

927
00:45:38,588 --> 00:45:41,628
which is just a new instance of this Hello World label. The 

928
00:45:41,628 --> 00:45:44,808
first thing I want to say is, "Hey, you know, I want to change what the font looks like." Anyone know 

929
00:45:44,809 --> 00:45:46,190
what font is. All 

930
00:45:46,190 --> 00:45:49,349
right, you've probably used different fonts in your word processors. It's just the way characters 

931
00:45:49,349 --> 00:45:52,068
actually appear on the screen. It's a thing that comes from type setting. 

932
00:45:52,068 --> 00:45:55,909
I want the font to be san seraph 36, 

933
00:45:55,909 --> 00:46:00,409
so what happens when I start off, is I say, "Create for me a new label 

934
00:46:00,409 --> 00:46:04,808
that's name is Hello World," and so it says, "Okay, I have some label object, the label with the 

935
00:46:04,809 --> 00:46:07,430
words associated with that label Hello World." Notice there's still nothing 

936
00:46:07,429 --> 00:46:11,379
on the screen. Here's my screen. Here's my canvas. This is all in the 

937
00:46:11,380 --> 00:46:14,499
computer's memory somewhere. It's saying, "Yeah, you've created some label. You haven't 

938
00:46:14,498 --> 00:46:16,038
displayed it yet. You've just created it," 

939
00:46:16,039 --> 00:46:21,139
and you say, "Hey I want to tell that label to change it's font to sans seraph 

940
00:46:21,139 --> 00:46:21,878
36." 

941
00:46:21,878 --> 00:46:23,739
The way I do that 

942
00:46:23,739 --> 00:46:27,869
is I have an object that I've created. The object is named label. 

943
00:46:27,869 --> 00:46:30,309
I use the name of the object 

944
00:46:30,309 --> 00:46:34,380
followed by a dot, followed by a method that I'm going to call on that object, 

945
00:46:34,380 --> 00:46:36,358
remember in Karel's world, we had methods. 

946
00:46:36,358 --> 00:46:39,809
The way we called Karel's methods was we just gave the name of the commands to go 

947
00:46:39,809 --> 00:46:41,219
execute that method. 

948
00:46:41,219 --> 00:46:46,358
Now, all methods are associated with objects, at least for the time being. So 

949
00:46:46,358 --> 00:46:49,818
when I have label and I say, "Set font," what that actually means 

950
00:46:49,818 --> 00:46:53,639
is set the fonts for this particular label object 

951
00:46:53,639 --> 00:46:57,328
to be Sans-Serif 36, and so when I execute that, 

952
00:46:57,329 --> 00:47:00,369
what happens is it becomes 36 point font 

953
00:47:00,369 --> 00:47:04,120
in Sans-Serif which means Serifs are just little things of 

954
00:47:04,119 --> 00:47:07,009
if you can see the font up there has you know, swishes at the end 

955
00:47:07,010 --> 00:47:10,360
of letters, those are serifs, so a font like this doesn't have any 

956
00:47:10,360 --> 00:47:13,959
of the squishes at the end of the letter. Sans-Serif, sans means not, Okay? 

957
00:47:13,958 --> 00:47:16,878
Then we say, "You know what, I'd really like you to be red because black is 

958
00:47:16,878 --> 00:47:19,518
just so blase and red is really the new black, 

959
00:47:19,518 --> 00:47:22,908
so set your color to be the red color." Like, 

960
00:47:22,909 --> 00:47:24,528
okay, and 

961
00:47:24,528 --> 00:47:27,909
so I execute that and it turns itself red. There's still nothing on the screen. This is all 

962
00:47:27,909 --> 00:47:31,608
like of with the label and now that I've taken this label and I've taken this text and 

963
00:47:31,608 --> 00:47:34,889
made it big and turned it red I finally say, "Hey, 

964
00:47:34,889 --> 00:47:40,289
graphics program, add this label, add this object to your collage," 

965
00:47:40,289 --> 00:47:44,759
and it says, "Okay," and it adds it at the location at which this label was created 

966
00:47:44,760 --> 00:47:46,939
which was 100,75. 

967
00:47:46,938 --> 00:47:51,349
So then it finally shows up on the screen. It only shows up on the screen when I actually do the add. 
 
969
00:47:51,349 --> 00:47:56,298
Up to that point, all I've done is modify some of the properties of this thing, okay. 

970
00:47:56,298 --> 00:48:00,599
So starting next time, what we're gonna actually get into is thinking about 

971
00:48:00,599 --> 00:48:03,068
what is this GLabel thing about, 

972
00:48:03,068 --> 00:48:07,159
what does it mean when we actually specify a method for an object and go into 

973
00:48:07,159 --> 00:48:10,548
all that in a little bit more detail, but hopefully seeing an example of what your 

974
00:48:10,548 --> 00:48:13,579
first Java program looks like. All right, I'll see you all on Wednesday.