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Week 2
Wed, Sept 5

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What are classes?
	fields + methods

What are objects: 
	Class definition + "instance data", or "state", for the fields
	
	Objects are very much like DATABASE RECORDS, 
	except for this public/private stuff.
	
How are objects created? 
	with new() and a "constructor"

Fig 1.6

Data types:
	int, String, classes

TicketMachine 2: how do you tell everything apart?
	_ convention??
	methods calling other methods
	
===============	
5. picdemo

	multiple ctors
		adding extra ctors to circle
		how they appear in bluej
		can one ctor call the other? sort of.
			
	
	First look at LOOPS
		meteor
		lawnzip -- oops, this probably isn't what we meant
		lawngrow
		Math.random()
		rain
			randombubbles
		
		Note use of RANDOM here that makes rain easier than lawngrow.
======================


accessors v mutators

if, if-else, if-else if - else
conditional 
Boolean

		
ClockDisplay example
ch 3: clock-display example.
	
	Abstraction
	two kinds of diagrams
	
		Can see the display updated by each timeTick by using the inspector.
		
		methods that call other methods
		object creation
		modularization & abstraction
		
		First, we want to build a display that increments correctly
		as "timeTick()" events (1-minute interval signals) arrive.
		
		We need hours:minutes. Why don't we make "hours" and "minutes"
		be NumberDisplay?
		
		Pros: good modularization/abstraction
		
		Cons: Maybe we can just *do* the thingie with numbers? 
			(but leading 0's are tricky)
			
		Consider a numberdisplay object, with an increment() method. 
		Note: % operator (read as "modulo"), and &&,
		and how to return a string from a number.
		
	
ClockDisplay object
	Note that we'll have different limits for the two NumberField thingies
	in a ClockDisplay.
	
	Numberdisplay:
		modulo operator
		"0" + num
		""  + num

	Now on to ClockDisplay. 
	1. Note updateDisplay() is *private*.
	Also, it's the first method we've had that is called by other methods
	of the same class.

	2. Objects creating subobjects
		look at the ctor
		initially "hours" and "minutes" are null
	

	3. Two different NumberDisplay subobjects, with different rolloverlimits
	
	4. multiple ctors for ClockDisplay
	
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Friday, Sept 7

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Examples: 
	picdemo	(pld's example, not a book example)
		train
		Picture
			meteor
			lawngrow
	MailSystem
	NoteBook
	
Structure of simple while loop:

	n=0;
	while (n<100) {
	    do stuff
	    do more stuff
	    ...
	    probably depends on n; may not though
	    
	    n=n+1;
	}
	
	used in lawngrow, rain, bubbles, meteor
	
		
		Some TABLES of numbers, using loops
		triangletable


============================================

Demo of MailSystem
	Note that it would be quite hard to simulate multiple users
	without the BlueJ object bench. 
	
	Look at MailItem
	Don't look at MailServer (why?)
	MailClient:
		"this" keyword: useful for dealing with name conflicts
		
	demo of creating three users and several messages, and
	using the Inspector
	
	demo of reading messages, and watching the inspector view change
	
	Demo of sending a message and setting a breakpoint in printNextMessage(),
	and running the debugger.

	(This crashed a couple times for me)
	
	5. Class diagrams v object diagrams
		class arrow: NOT just for subobjects
		
	What do the arrows mean for object diagrams? "Uses" relationship
		
    public void meteor(){
        Circle m = new Circle();
        ...
        int i = 0;
        while(i<150){
            m.moveHorizontal(2);
            m.moveVertical(1);
            i=i+1;
        }
    }

    public void rain(){
        Circle droplet;
        Random rand = new Random();
        int i=0;
        while(  i<100){
            int x = rand.nextInt(150);
            int y = rand.nextInt(200);
            droplet = new Circle(x,y);      // pld: new ctor
            droplet.changeColor("black");
            droplet.changeSize(4);
            droplet.makeVisible();
            i += 1;
        }
    }

    public void lawnzip() {
        Triangle t = new Triangle();
	...        
        while (i<24) {
            t.moveHorizontal(10);
            i=i+1;
        }
    }

    public void lawngrow() {
        Triangle t;
        int i = 0;
        while (i<24) {
            t = new Triangle();
            t.moveVertical(200);
            t.moveHorizontal(i*10);
            t.changeColor("green");
            t.changeSize(20,10);
            t.makeVisible();
            i=i+1;
        }
    }

    public void numtable() {		// Table of cubes
        int n=0;
        while(n<=20) {
            System.out.println(n  +  "  "  + n*n*n);
            n = n+1;
        }
       
    }