Stack Class

Extends the Vector class. Used to create a simple last-in-first-out stack.

·         An item is stored on a stack by ‘pushing’ it into the stack.

·         An item may subsequently be ‘popped’ off the stack and used.

·         A Stack object will grow in size as new items are pushed onto it.

Example:

import java.util.EmptyStackException;

import java.util.Stack;

public class StackDemo {

    Stack s;

    public StackDemo()
    {
      s = new Stack();
    }

    public static void main(String args[])
    {

      StackDemo objStackDemo = new StackDemo();

      objStackDemo.pushItem("Harry");

      objStackDemo.pushItem("Emaini");

      objStackDemo.pushItem("Voldmort");

      objStackDemo.pushItem("Snape");

      objStackDemo.pushItem("Dumbuldore");

      System.out.println();

      objStackDemo.popItem();

      objStackDemo.popItem();

      objStackDemo.popItem();

      objStackDemo.popItem();

      objStackDemo.popItem();

      try
      {

          objStackDemo.popItem();

      } catch(EmptyStackException e) {

          System.out.println("Exception : Empty Stack");

          }

    }

    void pushItem(String str)
    {

      s.push(str);

      System.out.println("Pushed : " + str);

      System.out.println("Stack has : " + s);

    }

    void popItem()
    {

       String str = (String)s.pop();

       System.out.println("Popped : " + str);

       System.out.println("Stack has : " + s);

    }

}

Queue Interface

public interface Queue extends Collection

– A collection designed for holding elements prior to processing.

– Queues typically order elements in a FIFO (first-in-first-out) manner.

– In a FIFO queue, all new elements are inserted at the tail of the queue.