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DefaultFocusTraversalPolicy.javaAPI DocJava SE 6 API4374Tue Jun 10 00:25:14 BST 2008java.awt

DefaultFocusTraversalPolicy

public class DefaultFocusTraversalPolicy extends ContainerOrderFocusTraversalPolicy
A FocusTraversalPolicy that determines traversal order based on the order of child Components in a Container. From a particular focus cycle root, the policy makes a pre-order traversal of the Component hierarchy, and traverses a Container's children according to the ordering of the array returned by Container.getComponents(). Portions of the hierarchy that are not visible and displayable will not be searched.

If client code has explicitly set the focusability of a Component by either overriding Component.isFocusTraversable() or Component.isFocusable(), or by calling Component.setFocusable(), then a DefaultFocusTraversalPolicy behaves exactly like a ContainerOrderFocusTraversalPolicy. If, however, the Component is relying on default focusability, then a DefaultFocusTraversalPolicy will reject all Components with non-focusable peers. This is the default FocusTraversalPolicy for all AWT Containers.

The focusability of a peer is implementation-dependent. Sun recommends that all implementations for a particular native platform construct peers with the same focusability. The recommendations for Windows and Unix are that Canvases, Labels, Panels, Scrollbars, ScrollPanes, Windows, and lightweight Components have non-focusable peers, and all other Components have focusable peers. These recommendations are used in the Sun AWT implementations. Note that the focusability of a Component's peer is different from, and does not impact, the focusability of the Component itself.

Please see How to Use the Focus Subsystem, a section in The Java Tutorial, and the Focus Specification for more information.

author
David Mendenhall
version
1.7, 11/17/05
see
Container#getComponents
see
Component#isFocusable
see
Component#setFocusable
since
1.4

Fields Summary
private static final long
serialVersionUID
Constructors Summary
Methods Summary
protected booleanaccept(java.awt.Component aComponent)
Determines whether a Component is an acceptable choice as the new focus owner. The Component must be visible, displayable, and enabled to be accepted. If client code has explicitly set the focusability of the Component by either overriding Component.isFocusTraversable() or Component.isFocusable(), or by calling Component.setFocusable(), then the Component will be accepted if and only if it is focusable. If, however, the Component is relying on default focusability, then all Canvases, Labels, Panels, Scrollbars, ScrollPanes, Windows, and lightweight Components will be rejected.

param
aComponent the Component whose fitness as a focus owner is to be tested
return
true if aComponent meets the above requirements; false otherwise


                                                                                                                                 
        
        if (!(aComponent.isVisible() && aComponent.isDisplayable() &&
	      aComponent.isEnabled()))
	{
	    return false;
	}

	// Verify that the Component is recursively enabled. Disabling a
	// heavyweight Container disables its children, whereas disabling
	// a lightweight Container does not.
	if (!(aComponent instanceof Window)) {
	    for (Container enableTest = aComponent.getParent();
		 enableTest != null;
		 enableTest = enableTest.getParent())
	    {
		if (!(enableTest.isEnabled() || enableTest.isLightweight())) {
		    return false;
		}
		if (enableTest instanceof Window) {
		    break;
		}
	    }
	}

	boolean focusable = aComponent.isFocusable();
	if (aComponent.isFocusTraversableOverridden()) {
	    return focusable;
	}

	ComponentPeer peer = aComponent.getPeer();
	return (peer != null && peer.isFocusable());