What is the use of FocusTraversalPolicy class?

[archer]

Hello friends,

I need your help to sort out my query related to the advanced java classes. I want to be aware about FocusTraversalPolicy class of java. I don't have any idea about the use FocusTraversalPolicy class. The methods of this class are also strange for me. If you have sound knowledge about the FocusTraversalPolicy class of java, then please let me know that. If possible then also give proper example for FocusTraversalPolicy class. I am waiting for your reply.

[Praetor]

A FocusTraversalPolicy defines the order in which Components with a particular focus cycle root are traversed. Instances can apply the policy to arbitrary focus cycle roots, allowing themselves to be shared across Containers. They do not need to be reinitialized when the focus cycle roots of a Component hierarchy change. The core responsibility of a FocusTraversalPolicy is to provide algorithms determining the next and previous Components to focus when traversing forward or backward in a UI. Each FocusTraversalPolicy must also provide algorithms for determining the first, last, and default Components in a traversal cycle.

[Katty]

Following java example will show you the use of FocusTraversalPolicy class:

import java.awt.FocusTraversalPolicy;
import javax.swing.SortingFocusTraversalPolicy;

public class FocusTDemo{

  public static void main(String argus[]) {
    JFrame FNT = new JFrame("Reverse Sample");
    FNT.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    FNT.setLayout(new GridLayout(3, 3));

    for (int i1 = 9; i1 > 0; i1--) {
      JButton button1 = new JButton(Integer.toString(i));
      FNT.add(button1, 0);
    }

    final Container contentPane1 = FNT.getContentPane();
    Comparator<Component> comp1 = new Comparator<Component>() {
      public int compare(Component c1, Component c2) {
        Component comps[] = contentPane1.getComponents();
        List listG = Arrays.asList(comps);
        int first1 = listG.indexOf(c1);
        int second1 = listG.indexOf(c2);
        return second1 - firs1t;
      }
    };
    FocusTraversalPolicy policy = new SortingFocusTraversalPolicy(comp1);
    FNT.setFocusTraversalPolicy(policy);

    FNT.setSize(300, 200);
    FNT.setVisible(true);
  }
}

[kelfro]

Hi,

Before using properties of FocusTraversalPolicy class, you need to be aware about following it's methods:

• getLastComponent(Container focusCycleRt)
• getInitialComponent(Window window)
• getFirstComponent(Container focusCycleRt)
• getDefaultComponent(Container focusCycleRt)
• getComponentBefore(Container focusCycleRt, Component Comp)

[Zecho]

Hi friend,

To know about the use of FocusTraversalPolicy class, I recommend you to review following java code:

import java.awt.FocusTraversalPolicy;
import javax.swing.JComponent;

public class FocusTraversalPolicyDM {
  public static Component smartRequestFocus(Component comp) {
    if (requestFocus(comp))
      return comp;
    if (comp instanceof JComponent) {
      FocusTraversalPolicy policy = ((JComponent) comp).getFocusTraversalPolicy();

      if (policy != null) {
        Component focusComponent = policy.getDefaultComponent((Container) comp);

        if (focusComponent != null && requestFocus(focusComponent)) {
          return focusComponent;
        }      }
    }
    if (comp instanceof Container) {
      Component[] children = ((Container) comp).getComponents();

      for (int ik = 0; ik < children.length; ik++) {
        comp = smartRequestFocus(children[i]);

        if (comp != null)
          return comp;
      }    }

    return null;
  }

  public static boolean requestFocus(Component comp) {
    return KeyboardFocusManager.getCurrentKeyboardFocusManager().getFocusOwner() == comp ||
           comp.requestFocusInWindow();
  }
}

[Reegan]

A FocusTraversalPolicy class comprises only one constructor known as 'FocusTraversalPolicy()'. A FocusTraversalPolicy class is taken from the 'java.awt.FocusTraversalPolicy' package. Which is subpart of 'java.lang.Object' package of java programming. Thre are two subclasses available with FocusTraversalPolicy class, which are ContainerOrderFocusTraversalPolicy and InternalFrameFocusTraversalPolicy. You can access properties of this java class using it's various methods.