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0) Last time- all about methods
- chapter 3 quiz

1) Administrative
- hw: continue A1
- read 4.5, 4.6, 4.10 (no presentations)

2) How to write an instantiable class

Program idea: simulate the second "hand" on a digital clock
Requirements: be able to "tick" the clock and display the time
Classes: main class (main method will be where we tell it to tick)
	   Counter class (will count ticks and wrap after hitting limit)

Counter class: (diagram)
	- data members: -count, +LIMIT
	- constructor: assigns initial values (constructors ALWAYS do)
	- methods: tick(), getCount(), printCount()

	* notice how the data members "belong" to the counter
	* private data, except unchangeable ones, and public methods
	* notice the difference between returning and printing

Main class: how we'll use a Counter (assume it exists) - coding now (online)
	Counter seconds = new Counter(60);
	seconds.tick();  seconds.printCount();
	seconds.tick();  int time = seconds.getCount();
	S.o.p("Clock has ticked " + time + " times.");
	S.o.p("Clock's limit is " + seconds.LIMIT + ".");

	* what you CAN'T do: seconds.count++;  (good, b/c might not wrap!)

Code Counter class now, and run it: outline comments first!

	public Counter(int limit) { LIMIT = limit; };
	public void tick() { int nextCount= (count+1)%LIMIT; count= nextCount;}

	* mod is a good way to do cyclical counting
	* note the local variables that don't exist anywhere else
	* but the data members are reachable from anywhere in the class
	* we DON'T re-declare the data members anywhere- only at the top
	* anywhere we say "count" there's an implicit "this.count"
	* we could have just used "60", but a constant is better (why?)

Memory diagram of main class, and program flow

3) Exercises to modify this class

	A) Keep track of the # of counter objects created using a data member.
		- how can we do that?  variable gets incremented in constructor
		- it has to be static (only one copy, not associated with object)
		- use it by making a getObjectCount() method and a minute counter
	
	B) Make it possible to start the count somewhere other than 0
		- make two constructors, so you can use either one
		- "overloading": same name, different parameters
		- change original to use this one so we don't duplicate code (this)
		- make sure it can't start at or past the limit! (use Math.min)
		- use it in main

	C) Make it possible to compare two counters and return the higher count.
		- method that takes another counter as parameter
		- compare this.count with parameter.count using Math.max

4) Summary
- pieces of an instantiable class and how to write them
- visibility, constants, and static members
- how data members and local variables are used in the methods
- how to make a class that fulfills specific requirements

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