1  import java.util.Stack;

  2  

  3  /**

  4     This program simulates an undo stack. Note that operations

  5     must be undone in the opposite order in which they are first

  6     issued.

  7  */

  8  public class StackDemo

  9  {

 10     public static void main(String[] args)

 11     {

 12        Stack<String> commands = new Stack<String>();

 13        commands.push("Insert 'Hello'");

 14        commands.push("Insert ','");

 15        commands.push("Insert ' '");

 16        commands.push("Insert 'World'");

 17        commands.push("Insert '?'");

 18        commands.push("Delete '?'");

 19        commands.push("Insert '!'");

 20  

 21        // Now we undo the last four commands

 22        for (int i = 1; i <= 4; i++)

 23        {

 24           String command = commands.pop();

 25           System.out.println("Undo " + command);

 26        }

 27     }

 28  }