FocusTraversalExample.java Source code

Introduction

Here is the source code for FocusTraversalExample.java

Source

/*
Java Swing, 2nd Edition
By Marc Loy, Robert Eckstein, Dave Wood, James Elliott, Brian Cole
ISBN: 0-596-00408-7
Publisher: O'Reilly 
*/

// FocusTraversalExample.java
//Similar to the FocusExample, this class uses the custom AlphaButtonPolicy
//focus traversal policy to navigate another small set of buttons.
//

import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.FocusTraversalPolicy;
import java.awt.GridLayout;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class FocusTraversalExample extends JPanel {

    public FocusTraversalExample() {
        setLayout(new GridLayout(6, 1));
        JButton button1 = new JButton("Texas");
        JButton button2 = new JButton("Vermont");
        JButton button3 = new JButton("Florida");
        JButton button4 = new JButton("Alabama");
        JButton button5 = new JButton("Minnesota");
        JButton button6 = new JButton("California");

        setBackground(Color.lightGray);
        add(button1);
        add(button2);
        add(button3);
        add(button4);
        add(button5);
        add(button6);
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("Alphabetized Button Focus Traversal");
        frame.setFocusTraversalPolicy(new AlphaButtonPolicy());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setContentPane(new FocusTraversalExample());
        frame.setSize(400, 300);
        frame.setVisible(true);
    }
}

//AlphaButtonPolicy.java
//A custom focus traversal policy that uses alphabetical ordering of button
//labels to determine "next" and "previous" buttons for keyboard traversal.
//

class AlphaButtonPolicy extends FocusTraversalPolicy {

    private SortedMap getSortedButtons(Container focusCycleRoot) {
        if (focusCycleRoot == null) {
            throw new IllegalArgumentException("focusCycleRoot can't be null");
        }
        SortedMap result = new TreeMap(); // Will sort all buttons by text.
        sortRecursive(result, focusCycleRoot);
        return result;
    }

    private void sortRecursive(Map buttons, Container container) {
        for (int i = 0; i < container.getComponentCount(); i++) {
            Component c = container.getComponent(i);
            if (c instanceof JButton) { // Found another button to sort.
                buttons.put(((JButton) c).getText(), c);
            }
            if (c instanceof Container) { // Found a container to search.
                sortRecursive(buttons, (Container) c);
            }
        }
    }

    // The rest of the code implements the FocusTraversalPolicy interface.

    public Component getFirstComponent(Container focusCycleRoot) {
        SortedMap buttons = getSortedButtons(focusCycleRoot);
        if (buttons.isEmpty()) {
            return null;
        }
        return (Component) buttons.get(buttons.firstKey());
    }

    public Component getLastComponent(Container focusCycleRoot) {
        SortedMap buttons = getSortedButtons(focusCycleRoot);
        if (buttons.isEmpty()) {
            return null;
        }
        return (Component) buttons.get(buttons.lastKey());
    }

    public Component getDefaultComponent(Container focusCycleRoot) {
        return getFirstComponent(focusCycleRoot);
    }

    public Component getComponentAfter(Container focusCycleRoot, Component aComponent) {
        if (!(aComponent instanceof JButton)) {
            return null;
        }
        SortedMap buttons = getSortedButtons(focusCycleRoot);
        // Find all buttons after the current one.
        String nextName = ((JButton) aComponent).getText() + "\0";
        SortedMap nextButtons = buttons.tailMap(nextName);
        if (nextButtons.isEmpty()) { // Wrapped back to beginning
            if (!buttons.isEmpty()) {
                return (Component) buttons.get(buttons.firstKey());
            }
            return null; // Degenerate case of no buttons.
        }
        return (Component) nextButtons.get(nextButtons.firstKey());
    }

    public Component getComponentBefore(Container focusCycleRoot, Component aComponent) {
        if (!(aComponent instanceof JButton)) {
            return null;
        }

        SortedMap buttons = getSortedButtons(focusCycleRoot);
        SortedMap prevButtons = // Find all buttons before this one.
                buttons.headMap(((JButton) aComponent).getText());
        if (prevButtons.isEmpty()) { // Wrapped back to end.
            if (!buttons.isEmpty()) {
                return (Component) buttons.get(buttons.lastKey());
            }
            return null; // Degenerate case of no buttons.
        }
        return (Component) prevButtons.get(prevButtons.lastKey());
    }
}