StackDemo shows how to use the linear set of objects

//--- 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