Programming Methodology-Lecture22

By Scott Perez,2014-02-04 11:31
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Programming Methodology-Lecture22 Programming Methodology-Lecture22

Programming Methodology-Lecture22

    Instructor (Mehran Sahami): Howdy! So welcome back to yet another fun-filled, exciting day of CS106a. Wee getting close to that

    Thanksgiving recess, which is always a good time. In the days of yore, it used not be a whole week. It used to be you got like one or two days off. You got like Thursday and Friday, which means you would have gotten only one day off from this class and now you get a whole week to mellow in style or catch up on all your other work as the case may be. So there one handout today. It Assignment No. 6, which is the next

    assignment, name, circle, watch. They talk a lot about that assignment in this class today. As a matter of fact, wee very fortunate for coming

    today because I will give you so much gratuitous information that presents that assignment. It just almost laughable.

    And then Assignment No. 5, as you know, is due today, so we can do painful to see how much time it actually took you. Just wondering, I heard from my little sources that exist was that last night, a lot of people were at the Lair and the computers at the Lair. Just wondering how many people were at the Lair last night. A fair number. And some of the computers at the Lair just mysteriously didn have Eclipse anymore. Anyone run into

    that problem? One person, okay.

    Yeah, there was some reimaging that went on, which I had nothing to do with and didn know about until some of the section leaders said, hey, Eclipse is missing on these machines and, you know, so I sent a very anxious email, I should say, to academic computing, and there had been some mix up and Eclipse is now reinstalled on all the machines, so I glad it

    didn affect too many people, but if it affected you, I apologize, although we really didn have anything to do with it, but I sorry that

    you had to experience that pain.

    So in terms of the painful, how much time it actually should give you the assignment on the Yahtzee assignment? Just wondering, how many of you actually liked the Yahtzee assignment? Just a quick show of hands. And how many thought it was just more pain than it was worth? Anyone? You folks, all right. And that good to know. I always try to ?actually try to gauge these things.

    So anyone in the zero to two-hour category? You just did it and it worked and life was good. Two to four? A couple people; that always good to

    see. Four to six? A reasonable contingent. Six to eight? Good times. Eight to ten? Wow, pretty healthy distribution there. Ten to twelve? Okay, wee falling off a bit. Twelve to fourteen? You folks. Fourteen to sixteen?

    Maybe a couple. Sixteen to eighteen? Eighteen plus? Taking a late day? Yeah.

    As you may have read ?I should refresh your memory because it pertains to Assignment No. 6, but as you may have read on Assignment ?on Handout No. 1 at the very beginning of class, because Assignment No. 7 is due the last day of the quarter, you can use late days on that assignment. So

    if you have late days and youe like, hey, I was just saving them up

    for No. 7, well, seven due the last day so there no classes beyond

    seven and you don say, hey, I taking a late day. That gives me an

    infinite amount of time to turn it in because there are no more classes. No, it doesn work like that.

    So Assignment No. 7 you can use late days on. So again, I would

    discourage you from using your late days, but should you have them and youe like, hey, I really wanna use my late days, Assignment No. 6 is kind of your last chance to actually use your free late days. Again, not that I would encourage you to use them, but just so you know up here that you don get Assignment 7 and say, hey, I thought I could use my late days for this. Youe getting plenty of advanced warning that you actually can.

    One other quick announcement; CS Career Panel is today, so after today, Il stop mentioning it because I believe most of you can actually

    time travel, so today, 5:30 p.m. in Packard 101. Be there. We have a stellar panel of folks from academia, from industry, a lot of people who actually ?every one is a computer science major and four of the five people graduated from Stanford department. The fifth is actually a faculty

    member here that didn graduate from my department, but is a faculty member here.

    And youl actually see there a very broad range of stuff to do. Out

    of those five people, though, actually, I think only one, maybe one and a half who actually do programming as their sort of fulltime job. But all of them are computer science undergraduates, so you get sort of a breadth of what computer sciences can do.

    So I so happy to see the fifth region. Youl see the variance gets

    larger, right. As the quarter goes on, that kind of happens, but it

    good to see that the mean is still where we generally want it to be. So now it time to talk a little bit about your next assignment. You just turned in your last assignment. Youe like, no, no, it not time

    to talk about the next assignment. I still working on the last

    assignment. Well, just pay attention.

Here what youe going to do for your next assignment. It a little

    program called NameSurfer, okay? And the idea of this program is it turns out that the government actually keeps track of statistics of the popularity of names over time, okay. So every decade when they do the census, they kind of keep track of the number of names and they rank the top 1,000 names in terms of popularity for boys?names and for girls?names, and they actually make this data available. We thought wouldn it be

    cool if you actually were to display names to the user in terms of how that popularity changed over time.

    So that what NameSurfer does. Here the program. What it does is it

    shows you the decades. You can notice that this is a graphics, or involves graphics, right, has the decades from 1900 up to 2000 and so relatively recent date up to the last census. And what we can do is we can type in a name and then click graph, and what it will do is it will show the rank of that name over time, on a decade-by-decade basis. So let try Fred,

    for example. If you graph Fred, you can see Fred real popular at the turn of the prior century and then Fred just had this quick decent into oblivion, where now he the 974th most popular boys name, at least in the last Census 2000. We can do multiple graphs on here, so if I type in someone else ?so one thing that also interesting is youl notice popular

    culture comes in, and so if I type in Britney, the alternative non-traditional British spelling, it didn exist until 1980, in which

    case it totally shot up to like the top 100 and maybe with the most recent things that are going on, it dropped a little bit.

    But through this whole region, what we have in our data, and Il show

    you the data in just a second, is that Britney did not rank in the top 1,000 until the 1980 and then it jumped up. Because it started ranking in the top 1,000 in the 1980, it still shows up in our data file because

    at some point it started ranking higher than that. And it turns out that there are some people who just have names that, well, are not so popular. So we do Mehran and nothing comes up because contrary to popular opinion, Mehran is not in the top 1,000 most popular names. In a few years, you can change that if you have children. Your choice. Not that I would advocate it, man. It a rough childhood. Mehran, doesn that sound like

    moron? Yeah, I haven heard that one in the last two hours. Yeah, I know. I just ?rough childhood. Not that it affected me at all. So in terms of actually doing this assignment, you might say, oh, that kind of

    interesting. Now there are a couple of things going on. You might look at that and say, yeah, I could do that, Mehran. I could do that in the zero to two-hour category, right, except for one little thing and the one little thing is check out this bad boy. Whoa. As I resize the window ?I will continue to resize the window until I get you in a hypnotic

    trance ?everything in the graphics display automatically resizes to display for that window size, okay? And what youe going to find out

    today is how do you actually do this kind of thing to keep track of as the windows resizing, how do you get events that come to your program that tell you, hey, some resizing happened. I need you to redisplay what

    going on.

    The other thing that interesting about this is I cannot only when I resize, it keeps track of all the information that on there, Fred and

    Britney. If I ask someone else like, oh, my son, William, who always

    been a popular choice ?ah ha ha ?just like in the top ten dips briefly over here because maybe it was getting over used and then it comes back up. Keeps them all. Theye in different colors. The color sort of cycles, so if we add someone else, like Ethel ?Ether, Ethel ?yeah, Ethel, sorry, not so popular anymore. When Lucille Ball ?when Love Lucy?was on or

    earlier, it was a popular time. The cycles of colors eventually will go back to black, so if we put in something like Bob, it goes back to black. Then youl see red again, then blue, then magenta. That all given

    to you in the handout.

    If you hit clear, everything goes away, except for the gridlines, and you can sort of go again from there, like here George and you can see George

    has a slight decline. Here four back here and now he like somewhere

     okay if it goes off the window occasionally, okay? in the hundreds. It

    But the resizing is kind of the key to this and that what wee going

    to ?one of the things wee gonna look at today. Okay.

    So that what you want to keep in mind for the assignment, resizing, because the demo that on the website because it runs in a web browser, doesn resize and it sort just has it as the little warning down at the bottom. It just shows you how the program actually works so you can try out typing in different names and see the behavior. But it doesn resize

    because its size it stuck by the browser and changing the browser window doesn actually change the size of the applet. That just life in the

    city, okay? But that the way NameSurfer works.

    So what we wanna think about is actually building programs that have this kind of property and to understand how programs that have this kind of property work, what we need to think about is something known as a component and related to that is a container. So first of all, Il show

    you all the classes in Java that pertain to the components and containers. Not all of them, but a good number of them. So here the classes in the

    component hierarchy and some of these will look familiar to you. So programs of which Console program and Graphics program that youe been

    using the whole time are j-applet, which is an applet, which is a panel, which is a container, which is a component.

    So somewhere all the way up the food chain, right, the food chain before we didn go that high. We just went up to applet when we showed you sort of this picture before. Turns out all your programs are components and containers. Every component is a container, or every container is a component. And so you may ask, well, what are containers and components? So the way you wanna think about this is at some generic level, a component is anything that can appear in a window. It anything that can in some

    sense be displayed. So your programs are appearing in a window that

    getting displayed. That why theye components, okay? Now, that also

    means that a graphics program and a console program are also components because theye subclasses of program. Now at the same time, there

    a notion of a container. What a container? A container is simply

    something that contains other components, so a container just contains a set of components and you might say, hey, Mehran, that really weird.

    A container is a component, but youe telling me it contains a set of

    components? What that all about? And the simplest way to think about it is it this, okay? This is a component, this bag. It turns out this bag is also a container because it contains things and it perfectly

    fine for something to be a container and also to be a component. So here what I mean, right. Your programs, as it turns out, are all components, which means they display in the screen, but theye also

    containers because your programs contain other things. For example, in the display of your program, it may contain a button. Right? It may also contain, say, a text field. And the other thing that it may contain, if you have a graphics program besides these kind of components, which buttons and text fields are also components ?Il show you an example

    of that in just a second ?it may contain another container. And it

    perfectly fine for containers to contain containers. As a matter of fact, youe been using them for the whole time. Your graphics program, especially if you have a graphics program that has some interactors on it. It could have buttons. It could have text fields. It could have a G-canvas, and gee, guess what? A G-canvas is a container and a component. Because it a component, it can be contained inside some other container, and because it itself is a container, it may have certain things in it. Oh, like here our friend, the frog image from the mid-term. Yeah, that was just something that was in another container, okay? So there no

    reason why something that is a container can be a component, which means

    it can be contained in some other container, that fine, and all

    containers themselves are components, so they can be stuck in somewhere else. That the basic idea. You should think of it as bags and you can

    put bags inside of other bags, and bags contain things. So even though you see the hierarchy this way, the concept itself is not actually that difficult. Now, the thing you wanna think about this is I just mentioned to you your programs are actually components and containers. G-canvas is a container and a component, but components that we talked about before, j-components, like our friends, say, oh, j-button ?you actually saw this slide a couple classes ago, j-button or j-label or j-combo box, all these

    you saw before ?are actually j-components. They all are subclasses things

    of j-component, which means by being subclasses of j-component, they were also containers, strangely enough, and they are also components. We just think of them generally as components and we try to put them in other containers, like we put them inside the display for a program and that its container. But that the general idea that kinda going on here.

    So when you wanna think about containers and components, what you also wanna think about is that these components themselves, before we thought about like action listeners, right, like something happens like I click on some component and some particular event happens, like I clicked on it, something like that. We can think of the whole component as also listening for other events because a component is something that display stuff on the screen.

    Stuff can happen to be components, like they can be resized and when a component resized, some event can get generated and sent to that component that says, hey, guess what? You got resized. You need to do something. Like the canvas that shows all the graphics, it can get some event that says, hey, canvas, yeah, you were just resized. Do whatever you wanna do. Up until now, you didn do anything. Someone came and

    resized your canvas. You said, yeah, youe resizing my canvas. All of

    the pieces I have in my canvas stay where they are. Nothing changing.

    Now what youe going to get is the ability to have the canvas be told, hey, you got resized or something else happened to you. You can respond to it however you want, which means you can redraw everything that in

    your canvas, so that, for example, you can have all the layout come out just fine when people resize your window. So what does that actually mean in terms of these components and containers? What it means is that we can have listeners in the same way that you kinda thought about listeners from mouse events and listeners for j-components. You can have listeners for components, okay, like we talked about resizing the window. Now, here a little simple example of something that can go on with one of these components. So Il come back to Eclipse, Il run a little

    program here ?I gotta compile ?and Il show you the very sort of simple

    program that makes use of this concept of a component having a listener and being able to get certain events. So it just called My Programming.

Here what my program does. It draws a square. That all it does is

    it draws in a filled-in square. Youe like why are you showing me this,

    Mehran? I coulde done this in the first week of class and I would say, no, you were doing terrible in the first week of class. And then you say, no, I coulde done this in the second week of class and be like, okay, but could you do this? Oh. Yeah, when you did this before, that square just stayed where it was and the size of the window changed. Nothing happened. Now the square always remains in the center of the window no

     super small. It still in the center. Super matter how I resize. It

    big, yeah. Another one of those things good for about 20 seconds. But that the idea. How does it know when the window getting resized that it

    needs to do something to update its display? So the way this is going to work, in terms of having this square that recenters itself, is we wanna think about having a program that is a container. And so, up until now, you had console programs and graphics programs, and they were containers and what they did for you automatically for console programming, it created a console for you and put it in your container so that anything you printed showed up in that console.

    And for a graphics program, it created a G-canvas for you and put it in the container and anything you drew showed up on that canvas. And now, what youe going to do is youe going to create your own program that

     not a graphics program or a console program, but to which youe going

    to create your own canvas and add it. And so the way that would look is you would say something like ublic Class?and give it the name, whatever name you want, so I call this y Program?and this is gonna extend just

    the generic program. It not gonna extend console or graphics program. It just gonna extend program. And so inside here, it still gonna have

    some init method, like youe come to know and love in other programs.

    And inside init, what wee gonna do is say I gonna create a new canvas.

    But the canvas I going to create is a canvas that is a new object I going to create myself to define what that canvas is, rather than the basic G-canvas. So I gonna call this My Canvas. I going to do top

    down design. My canvas is a class that doesn exist yet, all right? It

     not a built-in class. It my canvas. It something that I gonna

    write the code for in just a second and I gonna have some object called

    anvas,?which is off top My Canvas and I will create a new My Canvas. At this point, you should be getting a little bit worried unless youe internalized top down design. If youe internalized top down design,

    you say, yeah, I just gonna go create My Canvas when it time for me

    to write that code. For right now, I just going to assume it exists.

    And then what I gonna do is I going to add this canvas to my container. When I do an add of something that is a component, in this case, canvas

will be a component ?youl see why it a component in just a second ?it

    says, hey, program, add this particular element to yourself, and program says, hey, I a container, right? I don already have a canvas. I don

     already have a console, but I a container. Youe giving me a canvas,

    whoosh, the canvas goes up into my container, and if it the only thing

    in my container, its size will expand to fill up the whole screen. Kind of like you saw last time. And that it. So what Ie don in this

    program is said, hey, I gonna have a program. I gonna create a canvas

    where all the action isn gonna happen in that canvas, and I going

    to add that canvas to the display and then I gonna let the canvas do

    all the work. Is there any questions about this, just creating the canvas? So now we can actually sort of define what is My Canvas and Il show

    you that on the computer because it a little bit more involved. And

    you don need to worry about writing this all down. Actually, on Friday, Il give you a handout that has all this code in it. I just didn want

    to give it to you now because then you wouldn pay attention to what

     going on on the screen, okay? So what I gonna do is I gonna have

    canvas, so it going a class My Canvas. And My Canvas is going to be a G-

    to be an extension of a G-canvas. It gonna extend G-canvas. So all My

    Canvases are G-canvases. Because it a G-canvas, that means it a

    a component, I can add it to a container. So thatcomponent. Because it

     why add works there.

    Now, what am I gonna do with this thing? The other thing I wanna do is I wanna say, hey, this is a component that gonna listen for stuff, and

    so the way I do this is rather than doing add mouse listeners like I did before, or add action listeners, which look at actions of things like buttons, the way a component actually listens is it implements the component listener interface. So when you wanna have some component that is actually gonna get events that it listening for, component events,

    the way you do that is when you create the class, you say it implements component listener. That just the way you say it, so it going to

    implement the interface. There some set of methods it needs to provide

    that implement that interface and Il show you the list of methods real

    quickly. Theye just down here. These four methods here, component resize, component hidden, component moved, and component shown are the methods that comprise that interface, the component listener interface. So anything that implements the component listener interface needs to provide these four methods. In a lot of cases, you won necessarily care

    that something happened and so, for example, if the component is hidden, which means some other window comes over it, the component is moved, or the component is shown, youe like, yeah, whatever, like I don care.

    Those are good things. I need to have methods that correspond to those things because in order to implement the interface, I need to provide

    methods that correspond to all the methods that the interface is expecting, so I need to have these. But in three of these four cases, I not going

    to do anything, right? It just open brace, close brace.

    Someone comes along and says, hey, guess what? You know you were occluded. Someone hid you, so your component hidden, and youe like, yeah, that

     cool. Youe like, aren you going to do anything? No, I like hiding. And it like, oh, look, your component was moved. Someone came along and moved your window. Aren you gonna do something? And youe like,

    no. No, I cool with that. That fine. You moved me, all right? I won

     get into the music, but if you can think of that, what that reference actually is, it not that difficult. Louie, Louie. Component shown, again, definitely, so the only time we actually care about doing something is when wee resized because when wee resized, we wanna say, hey,

    our component was resized. Let me move that square to wherever the new center is of that window. So whenever my component resized, I gonna

    get the component resized method called and I just gonna call the method

    called Update. And what Update gonna do? Update right up here. All

    Update says is remove all, so who the remove all message being sent

    to? It being sent to myself because I not specifying any particular

    object to send this message to. So when I say remove all, I sending

    it to My Canvas. Well, My Canvas is a G-canvas, which means remove all, removes everything that on the canvas. It clears the canvas, which

    means wherever the square was before, it just got cleared. And what I gonna do is I gonna add some rectangle, and Il show

    pretty simple. So what I have is I have a private you the rectangle. It

    G-rect that I call rect. It just gonna be some private variable that

    I keep track of. In the constructor for my class, what I going to do

    is I gonna ?before I tell you what add component listener this does, I going to create a new rectangle, who width and height are whatever

    I specify as constants is the box width and box height. Theye just

    constants, not a big deal. And I set it to be filled. So what I get is a filled square. I created this rectangle as a filled square. I haven

    done anything yet with it other than create it, but Ie created it

    and I have some variable rect that refers to it. So all Update does is it says, hey, you know what? Remove the square if it was anywhere on the screen before and now add that rectangle back at the center location of the square, right? What the center location of this point? You should be good, real good, with figuring out how to center stuff on the screen. You take the width of the screen, subtract off the width of the object youe displaying, and divide by two. That the x location. You take

    the height of the screen, subtract off the height and divide by two. That the y location. And this get width and get height will get the current

    size of the component, which means when the components been resized, this update method gets called, it closed the screen, and it gets rid of the old box and draws a new box at wherever the new center of the screen is because this gets called, which means Update gets called after the component been resized. So that way it gonna redraw the square always

    in the center of the screen.

    The only other thing about this program that you need to know is in the constructor for My Canvas, My Canvas implements the component listener, so you not only need to say, hey, I implemented the component listener, but you need to let the ?you need to actually say, hey, you know what? I am a component listener, so add me to the component listener list, and the way it does that is you just call add component listener and you pass this, which means myself. So somewhere, I say, hey, you know what? Add me to the list of component listeners. I giving you a parameter to

    myself so you know who I am, so when something happens to me, you can call my component resize method to get resized. And that part up there, that Add Component Listener, is just a broiler plate, but it gonna, for

    example, show up in your NameSurfer assignment because guess what? In your NameSurfer assignment, when your component gets resized, youe going

    to do something very similar to this. Youe gonna find out what the new

    dimensions of the screen are and redraw everything that should actually be on the screen, which means you need to have some way of being able to keep track of the stuff that on the screen. So any questions about this?

    All righty, so that the basic notion of this idea of a component

    listener, okay, and what we wanna think about next is how do I create a larger program with these kind of things. So this is just the simple hint. Now I gonna give you something that even a bigger hint to what

    going on in NameSurfer.

    And so what I gonna do is one thing that real popular these days is

    kind of like music, right, like online music and albums and the whole deal. So what I wanna do is implement a program that keeps track of data related to music and at best, I gonna have a little music store, the program

    for the music score. And the basic idea here is that a lot of what ?well, I shouldn say a lot, but so far youe been ?I don know. You did

    a lot of games in this class and games are great and I totally encourage games, and I a big fan of games. I got into computer science because of games. It a good time. But a lot of what computers are actually used for as well, like when you go to some .dot com site or whatever to like buy music, and I won name a particular one because I might get sued, you know, it doing data management, right. For them, when you go to their site, all they really care about are what are the songs theye

    providing, do they ?you know, like youe buying a physical CD, do they

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