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Week 3
Mon, Jan 26

loops in Picture.java, numeric loops
Clockdisplay
MailSystem
Notebook

reprise:
	naming objects
		Lab-classes

picdemo:
	more loops
	numeric examples

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


accessors v mutators

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

Examples: 


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

		
    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;
        }
       
    }

Numeric example 
	
    public bool isPrime(int n) {
        int div = 2;
        int top = n-1; 	// top = (int) Math.sqrt(n)
        while (div < top) {
        	if (n % div == 0) return false;
        	div ++;
        }
        return true;
    }
   

now *print* primes from 1 to 100:

	for (int i = 1; i<=100; i++) {
	    if (isPrime(i)) {
	    	System.out.println("" + i + " is prime");
	    }
	}
		
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for loops / nested loops: OMIT FOR NOW

    public void triangletable() {
        int row,col;
        for (row = 1; row <= 15; row++) {
            for (col = 0; col<row; col++) {
                System.out.print("**");
            }
            System.out.println();
        }
    }

or:

    public void triangletable() {
        int row;
        for (row = 1; row <= 15; row++) {
            triangleRow(row*2);
        }
    }


    public void triangleRow(int width) {
    	int col;
        for (col = 0; col<width; col++) {
            System.out.print("*");
        }
        System.out.println();
    }

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4. ClockDisplay example
ch 3: clock-display example.
	
	Abstraction
	two kinds of diagrams: class and object.
	class ClockDisplay *uses* one other class, NumberDisplay.
	An object of type ClockDisplay *contains* two objects of type NumberDisplay.
	
		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. How about making "hours" and "minutes"
		be two separate instances of 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 %
			to check if n is even, we can check if (n % 2 == 0)
		"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

	5. NumberDisplay.setValue(): uses && operator ("and")
	
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Demo of MailSystem
	Note that it would be quite hard to simulate multiple users
	without the BlueJ object bench. 
	
	Look at MailItem

	MailClient:
		"this" keyword: useful for dealing with name conflicts
		
	demo of creating three users and several messages, and
	using the Inspector
		MailServer: *name* the object-bench instance ms1.
	
	MailServer:
		items: List<MailItem>
	loops:
		howManyMailItems(string who)
		for:each loop
		
		getNextMailItem(String who):
		Iterator loop in original version; could also be while loop
			do the while version
			forgot i++
			used <= instead of <
		
	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
		
	
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Wednesday

1. Different types on object bench: if they are to interact, 
their object-bench names MUST be used!
	Labclasses
	MailSystem
For that matter, two objects of the *same* type on the object bench must
have their names used somehow, in order to interact.

2. Notebook & chapter 4

3. Lab-classes revisited

================================================
The Notebook example will be made available to you during the first exam,
as a source of "standard" examples.

Notebook makes use of ArrayList, which can hold an arbitrary number of notes.

Notebook example:

Notebook1: 
	demo of storeNote, numberOfNotes, showNote
	look at code:
		ArrayList
		get/size
		inspector
	Problem: what if we forget which note we want?

Notebook2:
	A *loop* to show all notes
		while version
		for-each version
		(for loop, or "classic for loop", is also a possibility)
	
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Notebook search loop

javadoc and String page; find note.contains(s)

"return loop": use return statement to terminate when found
	isPrime was an example of this
	so was LabClass.searchStudent
	
"print all" loop: terminate at end of list, regardless of data found
	Notebook.searchNotes is an example
	
"find first" loop: compare to example on page 94
	
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Where else would this help?

	LabClass project
	
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