// Name:     Bradley Shedd
// Program:  LAB#11ExtraCredit
// Date:     December 1, 2010
// Class:    Java1302
// Filename: ArrayStack.java
// Purpose:  This class is an array-based Object stack class with operations push,
//           pop, and isEmpty and isFull.
// ****************************************************************

   public class ArrayStack implements StackADT
   {
      private int stackSize = 5;   // capacity of stack
      private int top;             // index of slot for next element
      private Object[] elements;     
  
    // --------------------------------------------------
    // Constructor -- initializes top and creates array
    // --------------------------------------------------
      public ArrayStack()
      {
         elements = new Object [stackSize];
         top = -1;
      }
  
    // --------------------------------------------------
    // Adds element to top of stack if it's not full, else
    // does nothing.
    // --------------------------------------------------
      public void push(Object val)
      {
         if ( isFull())
            increaseSize();
         elements[++top] = val;
      }
  
    // --------------------------------------------------
    // Removes and returns value at top of stack.  If stack
    // is empty returns null.
    // --------------------------------------------------
      public Object pop()
      {
         if (!isEmpty())
            return (elements[top--]);
         else
            System.err.println("Stack is empty!");
         return null;
      }
  
    // --------------------------------------------------
    // Returns true if stack is empty, false otherwise.
    // --------------------------------------------------
      public boolean isEmpty()
      {
         return ( top == -1 );
      }
  
    // --------------------------------------------------
    // Returns true if stack is full, false otherwise.
    // --------------------------------------------------
      public boolean isFull()
      {
         return ( top == ( stackSize - 1 ));
      }
   
      private void increaseSize()
      {
         Object [] temp = new Object [ 2 * elements.length];
         for ( int i = 0; i < elements.length; ++i)
            temp [i] = elements [i];
         elements = temp;
         stackSize  *= 2;
     }
  
  
   }

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