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Focus traversal based on alphabetical ordering of button labels |
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This Java tip illustrates a special way of traversing through buttons.
Normally, the traversing is done with the help of 'tab' key on keyboard in the same order in which button were designed. This method make the traversing possible on the basis of alphabetical
ordering of button labels.
import java.awt.*;
import java.util.*;
import javax.swing.*;
public 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());
}
}
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