//----------------------------------------------------------------
// ArrayStack.java       by Dale/Joyce/Weems             Chapter 3
//
// Implements BoundedStackInterface using an array to hold the 
// stack elements.
//
// ajg version: formatting,
//              just one constructor it is LEGAL, but weird
//                 (I call it the DWC--davis weird constructor)
//              protected->private, if-then-else
//----------------------------------------------------------------

package ch03.stacks;

public class ArrayStack<T> implements BoundedStackInterface<T> {
    private T[] stack;              // holds stack elements
    private int topIndex = -1;      // index of top element in stack

    public ArrayStack(T[] stack) { this.stack = stack; }
    
    public boolean isEmpty() { return topIndex == -1; }
    public boolean isFull()  { return topIndex == stack.length-1; }

    public void push(T element) {
	// Throws StackOverflowException if this stack is full,
	// otherwise places element at the top of this stack.
	if (isFull())
	    throw new StackOverflowException("Helpful msg.");
	else
	    stack[++topIndex] = element;
    }

    public void pop() {
	// Throws StackUnderflowException if this stack is empty,
	// otherwise removes top element from this stack.
	if (isEmpty())
	    throw new StackUnderflowException("Helpful msg.");
	else
	    stack[topIndex--] = null;
    }

    public T top() {
	// Throws StackUnderflowException if this stack is empty,
	// otherwise returns top element from this stack.
	if (isEmpty())
	    throw new StackUnderflowException("Helpful msg.");
	else
	    return stack[topIndex];
    }
}
// Local Variables:
// compile-command: "cd ../..; javac ch03/stacks/ArrayStack.java"
// End: