Computer Science 538
Lecture Notes for 5-3-00
Lecture by Professor Fischer
Notes by Michael Waddell

"Advanced" JAVA
---------------
I. Interfaces
II. Exceptions
III. Threads

I. Interfaces
-------------
Java only has single inheritance - not multiple inheritance.  BUT, it allows
multiple interfaces.

Interface Compare {
	Boolean LessThan(Object O1, Object O2);
}

Interfaces are just classes that lack implementation.  You implement them in 
other classes.

Class IntCompare Implements Compare {
	Boolean LessThan(Object i1, Object i2) {
		return ((Integer)i1).intVal() < ((Integer)i2).intVal();
	}
...
}

Class StringCompare Implements Compare {
	Boolean LessThan(Object s1, Object s2) {
		return ((String)s1).compareTo((String)s2) < 0;
	}
...
}

Class PrintCompare {
	static void printAns(Object v1, Object v2, Compare c) {
		System.out.println(v1 + "<" + v2 + "is" + c.LessThan(v1,v2);
	}
}

PrintCompare.printAns("abc", "xyz", new StringCompare);


II. Exceptions
--------------
All exceptions are subclasses of Throwable.

                   Throwable
                    /     \
             Exception    Error
              / 
        RunTimeException

Exceptions use a Try/Catch block syntax:

Try { ...
	Throw new Exception();
	...
	}
Catch(Exception) {System.out.println("Exception Caught!");
	}

Exceptions come in 2 types:
	Checked - you can't ignore this kind
	Unchecked - you can ignore them if you want, but they will terminate
			the program if uncaught

III. Threads
------------
Java supports multi-threading

This is very useful for GUIs, etc.

To use threading, you need a "Runnable" class.

Interface Runnable {
	public void run();
	}

Class PingPong implements Runnable{
	int delay;
	String word;
	PingPong(...) {...}
	public void run() {
		try {while(true) {System.out.println(word + " ");
			Thread.sleep(delay);
			}
		catch(interruptedExecution e) {}
		}
	public static void main(string args[]) {
		thread t1 = new thread(new PingPong(33,"ping");
		thread t2 = new thread(new PingPong(100,"pong");
		t1.start();
		t2.start();
		}
	}

output:
ping pong ping ping ping pong ping ping ping pong ...

Notice that although PingPong.run() seems like it would run forever, you can 
throw an exception at it that causes it to gracefully exit.

Continued on Friday...