//--- class StackDemo shows how to use the linear set of objects ---//
import java.applet.*;
import java.util.*;
import java.awt.*;
import java.awt.event.*;

public class StackDemo extends Applet {
 //--- Instance variables ---//
 Frame f;

 //--- Instance methods ---//
 public void init ()
 {
  f = new StackFrame ("Stack"); // instanciate a frame object
  f.setSize (200, 150);
  f.setResizable (false);
  f.show ();
 }

 public void start ()
 {
  f.setVisible (true);
  repaint ();
 }

 public void stop ()
 {
  f.setVisible (false);
 }

 public void paint (Graphics g)
 {
  g.drawString ("Ancestor object for the frame", 0, 30);
 }
}// end of class StackDemo

//--- class StackFrame ---//
class StackFrame extends Frame {

 StackPanel p;
 Stack stk;
 MessageBox mb;

 //--- Constructor ---//
 public StackFrame (String title)
 {
  super (title);

  //--- The object to handle action events ---//
  ActionListener al = new ActionHandler ();

  //--- Instanciate a panel object and add it into the frame ---//
  p = new StackPanel (al);
  add(BorderLayout.CENTER, p);

  //--- Instanciate a message box class ---//
  mb = new MessageBox (this, "Stack Message", al);

  //--- Instanciate stack class ---//
  stk = new Stack ();

  //--- anonimous inner class for handling window events ---//
  addWindowListener (new WindowAdapter (){
   public void windowClosing (WindowEvent e)
   {
    e.getWindow ().dispose ();
   }
  });
 }

 //--- Inner private class StackPanel ---//
 private class StackPanel extends Panel {
  //--- Instance variables ---//
  Label lblTitle;
  TextField tfStack;
  Button btnPush, btnPop, btnPeek;

  //--- Constructor ---//
  public StackPanel (ActionListener al)
  {
   super ();

   lblTitle = new Label ("Stack element");
   tfStack  = new TextField (25);
   btnPush  = new Button ("Push");
   btnPop   = new Button ("Pop ");
   btnPeek  = new Button ("Peek");

   add (lblTitle);
   add (tfStack);
   add (btnPush);
   add (btnPop);
   add (btnPeek);

   btnPush.addActionListener (al);
   btnPop.addActionListener (al);
   btnPeek.addActionListener (al);

   setBackground (Color.green);
  }
 }// end of class StackPanel

 //--- Inner class MessageBox ---//
 private class MessageBox extends Dialog {
  Label lbl;  // text to show in the dialog box
  Button btnOK; // botton OK

  //--- Constructor ---//
  public MessageBox (Frame parent, String title, ActionListener al)
  {
   super (parent, title, true); //call the ancestor constructor and make the dialog box modal
   setSize (100, 150);
   setBackground (Color.red);

   //--- Change the layout and add components into the container ---//
   setLayout (new FlowLayout ());
   add ( lbl = new Label ());
   add ( btnOK = new Button ("OK"));

   btnOK.addActionListener (al);
  }

  //--- Methods ---//
  public void showBox (String s)
  {
   lbl.setText (s);
   show ();
  }
 }// end class MessageBox

 //--- Inner class ActionHandler ---//
 private class ActionHandler implements ActionListener {
  public void actionPerformed (ActionEvent e)
  {
   Object source = e.getSource ();
   String s = p.tfStack.getText ();

   if (source == p.btnPush)
   {
    //--- If the tfStack is not empty than pust its content into the stack ---//
    if (!s.equals (""))
     stk.push (s);

    p.tfStack.setText ("");
    System.out.println ("Push");
    p.tfStack.requestFocus ();
   }

   else if (source == p.btnPop)
   {
    //--- If the stack is not empty, pop the element of the stack ---//
    if (!stk.empty ())
     p.tfStack.setText ((String) stk.pop ());
    else
    {
     p.tfStack.setText ("");
     mb.showBox ("Stack is empty");
    }

    System.out.println ("Pop");
    p.tfStack.requestFocus ();
   }

   else if (source == p.btnPeek)
   {
     //--- If the stack is not empty, pop the element of the stack ---//
    if (!stk.empty ())
     p.tfStack.setText ((String) stk.peek ());
    else
    {
     p.tfStack.setText ("");
     mb.showBox ("Stack is empty");
    }

    System.out.println ("Peek");
    p.tfStack.requestFocus ();
   }

   else if (source == mb.btnOK)
   {
    mb.dispose ();
   }
  }
 }// end of class ActionHandler
}// end of class StackFrame

Related:

• Interview Questions in Core Java - Part Two
• Java Interview Questions
• Interview Questions in Core Java

Return to : Java Programming Hints and Tips