DefaultFocusTraversalPolicy (Java Platform SE 6) - JDK 5 Documentation v6.0, Java 2 SDK 英文文档

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Java™ Platform
Standard Ed. 6

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java.awt
Class DefaultFocusTraversalPolicy

java.lang.Object
  java.awt.FocusTraversalPolicy
      java.awt.ContainerOrderFocusTraversalPolicy
          java.awt.DefaultFocusTraversalPolicy

All Implemented Interfaces:: Serializable

public class DefaultFocusTraversalPolicy
extends ContainerOrderFocusTraversalPolicy
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.

Since:: 1.4
See Also:: Container.getComponents(), Component.isFocusable(), Component.setFocusable(boolean), Serialized Form

Constructor Summary

DefaultFocusTraversalPolicy()

Method Summary

protected boolean accept(Component aComponent)
Determines whether a Component is an acceptable choice as the new focus owner.

Methods inherited from class java.awt.ContainerOrderFocusTraversalPolicy

getComponentAfter, getComponentBefore, getDefaultComponent, getFirstComponent, getImplicitDownCycleTraversal, getLastComponent, setImplicitDownCycleTraversal

Methods inherited from class java.awt.FocusTraversalPolicy

getInitialComponent

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Summary
`DefaultFocusTraversalPolicy()`

Method Summary
`protected boolean`	`accept(Component aComponent)` Determines whether a Component is an acceptable choice as the new focus owner.

Methods inherited from class java.awt.ContainerOrderFocusTraversalPolicy
`getComponentAfter, getComponentBefore, getDefaultComponent, getFirstComponent, getImplicitDownCycleTraversal, getLastComponent, setImplicitDownCycleTraversal`

Methods inherited from class java.awt.FocusTraversalPolicy
`getInitialComponent`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

DefaultFocusTraversalPolicy

public DefaultFocusTraversalPolicy()

Method Detail

accept

protected boolean accept(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.

Overrides:: accept in class ContainerOrderFocusTraversalPolicy

Parameters:: aComponent - the Component whose fitness as a focus owner is to be tested
Returns:: true if aComponent meets the above requirements; false otherwise