Find the previous focusable component : Focus « Swing Event « Java Tutorial






import java.awt.Component;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.FocusTraversalPolicy;
import java.awt.KeyboardFocusManager;

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

public class Main {
  public static void main(String[] argv) {
    JFrame frame = new JFrame();
    JButton component1 = new JButton("1");
    JButton component2 = new JButton("2");
    JButton component3 = new JButton("3");

    frame.setLayout(new FlowLayout());
    frame.add(component1);
    frame.add(component2);
    frame.add(component3);

    frame.pack();
    frame.setVisible(true);

    System.out.println(findPrevFocus().getName());
  }

  public static Component findPrevFocus() {
    Component c = KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner();
    Container root = c.getFocusCycleRootAncestor();

    FocusTraversalPolicy policy = root.getFocusTraversalPolicy();
    Component prevFocus = policy.getComponentBefore(root, c);
    if (prevFocus == null) {
      prevFocus = policy.getDefaultComponent(root);
    }
    return prevFocus;
  }
}








15.15.Focus
15.15.1.No Focus Button
15.15.2.Focus auto-settingFocus auto-setting
15.15.3.Focus Traversal: requestFocusInWindowFocus Traversal: requestFocusInWindow
15.15.4.Moving focus to the next component: focusNextComponent()Moving focus to the next component: focusNextComponent()
15.15.5.Restricting the Focus CycleRestricting the Focus Cycle
15.15.6.Request Focus inside a windowRequest Focus inside a window
15.15.7.Predefined Focus Traversal Policies
15.15.8.Reversing Focus TraversalReversing Focus Traversal
15.15.9.KeyboardFocusManagerKeyboardFocusManager
15.15.10.Use KeyboardFocusManagerUse KeyboardFocusManager
15.15.11.Use FocusTraversalPolicy
15.15.12.Finding the Next Focusable Component
15.15.13.Find the previous focusable component
15.15.14.Determining If a Focus Lost Is Temporary or Permanent
15.15.15.Null is returned if none of the components in this application has the focus
15.15.16.Null is returned if none of the windows in this application has the focus
15.15.17.Changes the focus traversal keys for the entire application.
15.15.18.Change the backward focus traversal keys for the application
15.15.19.Change the forward focus traversal keys for a component
15.15.20.JComponent.setFocusTraversalKeys(int arg0, Set arg1)
15.15.21.KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS
15.15.22.Setting Focus Traversal Keys for the Entire Application
15.15.23.KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS
15.15.24.KeyboardFocusManager.getCurrentKeyboardFocusManager().getDefaultFocusTraversalKeys(KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS)
15.15.25.KeyboardFocusManager.getCurrentKeyboardFocusManager().clearGlobalFocusOwner()
15.15.26.Determining the Opposite Component of a Focus Event
15.15.27.Listening to All Key Events Before Delivery to Focused Component
15.15.28.Removing the Focus from the Application
15.15.29.Use isFocusOwner to determine whether a particular component has the focus
15.15.30.JComponent.WHEN_IN_FOCUSED_WINDOW
15.15.31.Make sure that my Text field has the focus when a JFrame is created