the Stack

 // stack.java
// demonstrates stacks
// to run this program: C>java StackApp
////////////////////////////////////////////////////////////////
class StackX
   {
   private int maxSize;        // size of stack array
   private long[] stackArray;
   private int top;            // top of stack
//--------------------------------------------------------------
   public StackX(int s)         // constructor
      {
      maxSize = s;             // set array size
      stackArray = new long[maxSize];  // create array
      top = -1;                // no items yet
      }
//--------------------------------------------------------------
   public void push(long j)    // put item on top of stack
      {
      stackArray[++top] = j;     // increment top, insert item
      }
//--------------------------------------------------------------
   public long pop()           // take item from top of stack
      {
      return stackArray[top--];  // access item, decrement top
      }
//--------------------------------------------------------------
   public long peek()          // peek at top of stack
      {
      return stackArray[top];
      }
//--------------------------------------------------------------
   public boolean isEmpty()    // true if stack is empty
      {
      return (top == -1);
      }
//--------------------------------------------------------------
   public boolean isFull()     // true if stack is full
      {
      return (top == maxSize-1);
      }
//--------------------------------------------------------------
   }  // end class StackX
////////////////////////////////////////////////////////////////
class StackApp
   {
   public static void main(String[] args)
      {
      StackX theStack = new StackX(10);  // make new stack
      theStack.push(20);               // push items onto stack
      theStack.push(40);
      theStack.push(60);
      theStack.push(80);

      while( !theStack.isEmpty() )     // until it's empty,
         {                             // delete item from stack
         long value = theStack.pop();
         System.out.print(value);      // display it
         System.out.print(" ");
         }  // end while
      System.out.println("");
      }  // end main()
   }  // end class StackApp
////////////////////////////////////////////////////////////////