So really it may feel like in this unit there's a lot more new things or maybe they wouldn't feel like things are quite as tightly tied to your understanding of blocks. That's I think a little bit true but it's not in the conceptual sense. The conceptual sense of hey, we have sprites or we have objects and we can give them methods which are lists of instructions that they can do, when they do those things, that's going to be true. That's what we're going to be doing here in Java. There is a lot more sort of syntactic detail that you have to go into in terms of creating that because you're not clicking on the apple and saying give me a new apple. As we go into the concepts and the remainder of the units with the exception of unit 5, we're going to get back to much more closely aligned to box, so don't worry about that. So in this particular unit we're going to be looking at three different classes. So maybe remember going back we could have had class apple, we could have had class turtle, we could have a lot of whatever. We're going to be looking at string class, the math class, and then two classes that are related, they're called wrapper classes. You don't need to know that vocabulary just yet, Integer and double. These are all provided with general of the note what we call the [inaudible] Java that you would install, and so that's why these are going to be used significantly in the APCS principle or CSA course. But we're also in CS Awesome going to be looking at some other pre-defined classes. So classes that we are not going to have to know how to create them ourselves, we're just going to use them a lot like we did maybe in scratch or snap, and in particular we've got our good old friend Turtle which if you've done Pencilcode.net are really almost anything even Code.org giving directions to different, the angry Bird or something. That's a lot like turtle and giving directions to a turtle. So there's a lot of things that I'm not going to go into detail on all of them because again it's about the details but there's one big principle that I want to bring up that's radically different, and that is that Java runs a single script. Remember you could write multiple scripts associated with one particular object and they could run all in parallel or maybe you had multiple objects and they each had when the green flag is clicked thing. So that once you click that green flag there might be lots of different sprites or objects executing their own code simultaneously. That's not going to be true in Java, you can't make that happen but not in this course. We have, this is just from the last unit once or something you've seen before in the last programming problems. We've a single script if you want to think of it. It's main. It's called main and whenever we run our code it's going to do just these sets of instructions. Some of these are actually calling other methods like print line. It turns out is a method that you're calling that's got other things that go in it, but we're just going do this one set of things. There's not like a bunch of mains they're going to start off at the same time. To move to an example that you're going be working with next. Again, you're going to have this single script, this is now called a program, okay. We do not use the word script particularly in the Java world. This is a program, it's in our main method and what you see here that we're going to get used to is we're going to be creating our own objects. So we're going to create and use multiple different objects; remember objects is like sprite in one program. Here we're going two Turtle's one is named Yertle and one is Myrtle, and they're going to both be; when we say new that's going to be creating those new turtle objects for us. That leads a little bit more complication because if we have more than one object or sprite in our particular program we're going to have to not just say forward or turn left, we are going to have to say which object should go forward, which object should turn left, and so the first one Yertle.forward. That means it's the Yertle object version of forward or myrtle.turn right maybe it's that. The other thing that you might have is that we're going to have more different classes and more objects than used to. So usually we were all just focused on the turtle row. Here we have to create a new world object. It's a world-class and maybe you like this maybe you don't, it is common in Java. The capital W world, that's our class and that lowercase world W-R-O-L-D, the second word in that line, that's an object, and I know that people say, "Why would you give it the same name?" I don't know exactly. I like my world better but it is common. So we're going to be not just having maybe just turtles but we're going to have to have a World and then sometimes we're going to have to do magic things with some of those just to make our code be interesting and this is for example something you'll see. We're always going to have to say world.show parentheses true that's calling on the world object, calling the method show and passing a parameter true. So that's saying we actually want to show the output of what was going on but they'll be some magic here. The other thing is I want to point out about magic is that this is Unit 2, and if you look at the title of it we call it Using Objects. You're actually also using classes. I don't know the reason why they didn't decide to include both of those. So mostly when we were dealing with scripts here we, Sorry. Mostly when we were in block-based programs we started off just using those existing classes, or sorry existing methods that came with our objects like forward turn, right turn whatever and we're going do that here. But later on we went into making our own blocks or etc. We're going to do that in Unit 5. So in Unit 5 we're going to create our own classes and that means defining not only the methods that we're going to use. We're actually going to define what those objects are and what kinds of things. So we're going to have later, we're going to find out about how to write our own classes and use those objects. So to summarize, we're going do just the using of methods from objects now to make things happen, and we'll figure out how that gets done underneath or how we make our own blocks later.
