• A TextField which can be used to input the size of Hanoi tower. When Enter was pressed in this TextField, the applet begins to show steps to solve Hanoi tower.
• Three graphics objects each rendering a pile of disks.

• A component constrols the execution speed, such that users can see clearly how disks were moved.
• Some fancy behaviors, such as flying disks between stacks.
• Different colors for moving disks.
• Another button for execution instead of the TextField.

• A pile of disks works like a stack. So you may create a class Pile with push and pop methods.
• Extends Canvas or Component to create a graphics object.

/* Program Name: Pile.java
 * Subject: Maintain and render a pile of disks
 * Author: Shiuh-Sheng Yu
 *         National ChiNan University
 *         Department of Information Management
 * Since: 1999/03/20
 * ToolKit: JDK1.1
 */
import java.awt.*;
public class Pile extends Canvas {
    private int top;
    private int[] data;
    public Pile(int initDisks) {
        super(); 
        // initialize your data at follows
    }
    /**
     * Push a disk of size n to this pile.
     * This method enfoces screen update ASAP.
     * @param size the size of the disk
     */
    public void push(int size) {
        // maintain your data structure
        repaint();
    }
    /**
     * Pop out a disk. This method enfoces screen update ASAP.
     * @return size of the disk on top of the pile
     */
    public int pop() {
        // maintain your data structure
        repaint();
        // return the top disk
    }
    /**
     * Draw disks of the pile on Graphics g
     * /
    public void paint(Graphics g) {
        g.setColor(Color.blue);
        // set any color you likes
        // draw stick here
        g.setColor(Color.red);
        // set any color you likes
        // draw disks here
    }
}

/**
 * Program Name: AddConstraint.java
 * Subject: GridBagLayout utility
 * Author: Shiuh-Sheng Yu
 *         National ChiNan University
 *         Department of Information Management
 * Since: 06/14/1997
 * Modify Date: 03/21/1999, add more comments
 * ToolKit: JDK1.1
 */
public class AddConstraint {
    public static void addConstraint(Container container, Component component,
          int grid_x, int grid_y, int grid_width, int grid_height,
          int fill, int anchor, double weight_x, double weight_y,
          int top, int left, int bottom, int right) {
        GridBagConstraints c = new GridBagConstraints();
        c.gridx = grid_x; c.gridy = grid_y;
        c.gridwidth = grid_width; c.gridheight = grid_height;
        c.fill = fill; c.anchor = anchor;
        c.weightx = weight_x; c.weighty = weight_y;
        c.insets = new Insets(top,left,bottom,right);
        ((GridBagLayout)container.getLayout()).setConstraints(component,c);
        container.add(component);
    }
}

/**
 * Program Name: Hanoi.java
 * Subject: An applet shows how to solve Hanoi tower problem
 * Author: Shiuh-Sheng Yu
 *         National ChiNan University
 *         Department of Information Management
 * Since: 1999/03/20
 * Modify Date: 3/21/1999, add more comments
 * Toolkit: JDK1.1
 */
import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
public class Hanoi extends Applet implements ActionListener, Runnable {
    TextField input;
    Pile a=null, b=null, c=null;
    Panel display;
    int size;
    // Setup GUI
    public void init() {
        this.setLayout(new GridBagLayout());
        AddConstraint.addConstraint(this, 
            new Label("Enter integer and press Enter:"), 0, 1, 1, 1, 
            GridBagConstraints.NONE,
            GridBagConstraints.WEST,
            0,0,0,0,0,0);
        AddConstraint.addConstraint(this,
            input = new TextField(10), 1, 1, 1, 1,
            GridBagConstraints.NONE,
            GridBagConstraints.WEST,
            0,0,0,0,0,0);
        input.addActionListener(this);
        AddConstraint.addConstraint(this,
            display = new Panel(), 0, 0, 2, 1,
            GridBagConstraints.BOTH,
            GridBagConstraints.CENTER,
            1,1,0,0,0,0);
        display.setLayout(new GridLayout(1,3));
        input.requestFocus();
    }
    // process user's action in TextField input
    public void actionPerformed(ActionEvent e) {
        try {
            size = Integer.parseInt(e.getActionCommand());
            if (size > 0) {
                display.removeAll();
                display.add(a = new Pile(size));
                display.add(b = new Pile(0));
                display.add(c = new Pile(0));
                // Ensures that this component has a valid layout.
                display.validate();
                // Creates a thread to move our disks.
                // So that we can return control back immediately to window system.
                (new Thread(this)).start();
            }
        } catch(NumberFormatException ex) { // not a number in TextField
            input.setText("");
        }
    }
    // starts to move disks
    public void run() {
        move(size, a, b, c);
    }
    // recursively solve the Hanoi problem
    private void move(int n, Pile from, Pile to, Pile free) {
        if (n > 0) {
            // move n-1 disks
            // move 1 disk
            try { // sleep 1 second to let users see what happened
                Thread.currentThread().sleep(1000);
            } catch(InterruptedException ex) {
            }
            // move n-1 disks
        }
    }
}