https://sites.google.com/site/drjohnbmatthews/keypad-panel


The example below shows how to use actions and key bindings to implement a simple numeric keypad in Java. The digits entered are displayed as they are typed. The numeric buttons are disabled if the number of digits typed exceeds an arbitrary limit—seven in the picture shown. The Clear action simply clears the entered text and re-enables all the buttons. The Enter action examines the finished entry and forwards the action to Clear. A third action, Click, enables the numeric keys to emulate clicking the number buttons. Note how a single action may be bound to more than one key—in this case, the numbers on the keyboard or keypad. Addition details may be found in the article Keyboard Bindings in Swing. The article Key Bindings is also very helpful; it includes more examples and a convenient utility.
package gui;

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.KeyStroke;

/**
 * A numeric key pad panel using <code>Action</code> with key bindings.
 * 
 * @author John B. Matthews; distribution per LGPL
 */
public class KeyPadPanel extends JPanel {

    private int maxDigits = 10;
    private final JTextArea text = new JTextArea(1, maxDigits);
    private final JButton clear = new JButton(new Clear("Clear"));
    private final JButton enter = new JButton(new Enter("Enter"));
    private final List<NumberButton> numbers = new ArrayList<NumberButton>();

    /**
     * Construct a numeric key pad that accepts up to ten digits.
     */
    public KeyPadPanel() {
        super(new BorderLayout());

        JPanel display = new JPanel();
        text.setFont(new Font("Dialog", Font.PLAIN, 24));
        text.setEditable(false);
        text.setFocusable(false);
        display.add(text);
        this.add(display, BorderLayout.NORTH);

        JPanel pad = new JPanel(new GridLayout(4, 3));
        for (int i = 0; i < 10; i++) {
            NumberButton n = new NumberButton(i);
            numbers.add(n);
            if (i > 0) {
                pad.add(n);
            }
        }
        pad.add(clear);
        clear.setFocusable(false);
        this.getInputMap().put(KeyStroke.getKeyStroke(
            KeyEvent.VK_CLEAR, 0), clear.getText());
        this.getActionMap().put(clear.getText(), new Click(clear));
        pad.add(numbers.get(0));
        pad.add(enter);
        enter.setFocusable(false);
        this.getInputMap().put(KeyStroke.getKeyStroke(
            KeyEvent.VK_ENTER, 0), enter.getText());
        this.getActionMap().put(enter.getText(), new Click(enter));
        this.add(pad, BorderLayout.CENTER);
    }

    /**
     * Construct a numeric key pad that accepts up to <code>maxDigits<code>.
     */
    public KeyPadPanel(int maxDigits) {
        this();
        this.maxDigits = maxDigits;
        this.text.setColumns(maxDigits);
    }

    private class Clear extends AbstractAction {

        public Clear(String name) {
            super(name);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            text.setText("");
            for (NumberButton n : numbers) {
                n.setEnabled(true);
            }
        }
    }

    private class Enter extends AbstractAction {

        public Enter(String name) {
            super(name);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("Entered: " + text.getText());
            clear.getAction().actionPerformed(e);
        }
    }

    private class Click extends AbstractAction {

        JButton button;

        public Click(JButton button) {
            this.button = button;
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            button.doClick();
        }
    }

    /*
     * A numeric button with digit key bindings that appends to
     * <code>text<code>, accepting no more than <code>maxDigits<code>.
     */
    private class NumberButton extends JButton {

        public NumberButton(int number) {
            super(String.valueOf(number));
            this.setFocusable(false);
            this.setAction(new AbstractAction(this.getText()) {

                @Override
                public void actionPerformed(ActionEvent e) {
                    String cmd = e.getActionCommand();
                    if (text.getText().length() < maxDigits) {
                        text.append(cmd);
                    }
                    if (text.getText().length() == maxDigits) {
                        for (NumberButton n : numbers) {
                            n.setEnabled(false);
                        }
                    }
                }
            });
            KeyPadPanel.this.getInputMap().put(KeyStroke.getKeyStroke(
                KeyEvent.VK_0 + number, 0), this.getText());
            KeyPadPanel.this.getInputMap().put(KeyStroke.getKeyStroke(
                KeyEvent.VK_NUMPAD0 + number, 0), this.getText());
            KeyPadPanel.this.getActionMap().put(this.getText(), new Click(this));
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                JFrame f = new JFrame();
                f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                f.add(new KeyPadPanel(7));
                f.pack();
                f.setLocationRelativeTo(null);
                f.setVisible(true);
            }
        });
    }
}

Copyright:

©2011, John B. Matthews. Distribution permitted without warranty under the terms of the LGPL.

Last updated 27-Jun-2011

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