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package java.awt;
import java.awt.peer.ComponentPeer;
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 See Also: Since: 1.4
/**
* 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
* <code>Container.getComponents()</code>. Portions of the hierarchy that are
* not visible and displayable will not be searched.
* <p>
* If client code has explicitly set the focusability of a Component by either
* overriding <code>Component.isFocusTraversable()</code> or
* <code>Component.isFocusable()</code>, or by calling
* <code>Component.setFocusable()</code>, 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.
* <p>
* 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.
* <p>
* Please see
* <a href="https://docs.oracle.com/javase/tutorial/uiswing/misc/focus.html">
* How to Use the Focus Subsystem</a>,
* a section in <em>The Java Tutorial</em>, and the
* <a href="../../java/awt/doc-files/FocusSpec.html">Focus Specification</a>
* for more information.
*
* @author David Mendenhall
*
* @see Container#getComponents
* @see Component#isFocusable
* @see Component#setFocusable
* @since 1.4
*/
public class DefaultFocusTraversalPolicy
extends ContainerOrderFocusTraversalPolicy
{
/*
* serialVersionUID
*/
private static final long serialVersionUID = 8876966522510157497L;
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.
Params: - aComponent – the Component whose fitness as a focus owner is to
be tested
Returns: true if aComponent meets the above requirements;
false otherwise
/**
* 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
* <code>Component.isFocusTraversable()</code> or
* <code>Component.isFocusable()</code>, or by calling
* <code>Component.setFocusable()</code>, 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 <code>true</code> if aComponent meets the above requirements;
* <code>false</code> otherwise
*/
protected boolean accept(Component aComponent) {
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());
}
}