What is an abstract data type?

Why define abstract data types?

What are the advantages of information hiding?

What are the advantages of encapsulation?

What is the difference between a class and an object?

What is the difference between a class and a (Java) package?
We probably won't do much with packages because they require a directory hierarchy.

Here is "almost stub" version of Throttle class

public class Throttle
{
	private int top;
	private int position;
	public Throttle(int size) { }
	public double getFlow( ) { }
	public boolean isOn( ) { }
	public void shift(int amount) { }
	public void shutOff( ) { }
}

Why did I say "almost" stub?
What additional code would be required to make this a "stub of a class"?
What is the constructor?
What are the methods?
What are the instance variables?
Why are some components public and others private?
What purpose would a private method serve?
What file would this class definition be stored in?

Here is a driver to test the class (also see ThrottleDemonstration on page 60):

import Throttle;

public class ThrottleDriver
{
	public static void main(String args[])
	{
		final int HIGH_POSITION = 10;	// what does "final" mean?
		Throttle myControl;		// what is value of myControl?
		myControl = new Throttle(HIGH_POSITION);
		Throttle yourControl = myControl;	// what happens here?
		myControl.shift(2);
		if (myControl == yourControl) 
			System.out.println("same");
		else
			System.out.println("different");
		// What is output of above 'if' statement?
		yourControl = new Throttle(HIGH_POSITION); // what happens here?
		yourControl.shift(2);
		if (myControl == yourControl) 
			System.out.println("same");
		else
			System.out.println("different");
		// What is output of above 'if' statement?
		if (myControl.getFlow() == yourControl.getFlow()) 
			System.out.println("same");
		else
			System.out.println("different");
		// What is output of above 'if' statement? Any peril here?
		int upward = 5;
		testAndShift(myControl, upward); 
		System.out.println(myControl.getFlow());
		System.out.println(upward);
		// What are the outputs of these two?  Why?
	}
	
	static int testAndShift(Throttle control, int val)
	{
		int result = 0;
		if (control.isOn())
		{
			control.shift(val);
			result = val;
		}
		val = result;	// unnecesary, used for arg. demonstration.
		return result;
	}
}

Here is complete Throttle source code, also found on textbook page 58.

public class Throttle
{
	private int top;
	private int position;
	public Throttle(int size)
	{
		if (size <= 0)
			throw new IllegalArgumentException("Size<=0"+size);
		top = size;
		// position automatically initialized to 0
	}
	public double getFlow( )
	{
		return (double) position / (double) top; 
		// what does "(double)" mean and why used?
	}
	public boolean isOn( )
	{
		return (getFlow( ) > 0); // Some prefer "this.getFlow( )"
	}
	
	public void shift(int amount)
	{
		if (amount > top - position)
		// adding amount would put position over the top
			position = top;
		else if (position + amount < 0)
			// adding amount would put position below zero.
			position = 0;
		else
			position += amount;
	}
	public void shutOff( )
	{
		position = 0;
	}
}

[ Lectures | CSC 132 | Peter Sanderson | Computer Science | SMSU ]

Peter Sanderson ( PeteSanderson@smsu.edu )