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package java.awt;
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. First and last Components are used when normal forward and
backward traversal, respectively, wraps. The default Component is the first
to receive focus when traversing down into a new focus traversal cycle.
A FocusTraversalPolicy can optionally provide an algorithm for determining
a Window's initial Component. The initial Component is the first to receive
focus when a Window is first made visible.
FocusTraversalPolicy takes into account focus traversal
policy providers. When searching for first/last/next/previous Component,
if a focus traversal policy provider is encountered, its focus traversal
policy is used to perform the search operation.
Please see
How to Use the Focus Subsystem,
a section in The Java Tutorial, and the
Focus Specification
for more information.
/**
* 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.
* <p>
* 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. First and last Components are used when normal forward and
* backward traversal, respectively, wraps. The default Component is the first
* to receive focus when traversing down into a new focus traversal cycle.
* A FocusTraversalPolicy can optionally provide an algorithm for determining
* a Window's initial Component. The initial Component is the first to receive
* focus when a Window is first made visible.
* <p>
* FocusTraversalPolicy takes into account <a
* href="doc-files/FocusSpec.html#FocusTraversalPolicyProviders">focus traversal
* policy providers</a>. When searching for first/last/next/previous Component,
* if a focus traversal policy provider is encountered, its focus traversal
* policy is used to perform the search operation.
* <p>
* Please see
* <a href="http://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#setFocusTraversalPolicy
* @see Container#getFocusTraversalPolicy
* @see Container#setFocusCycleRoot
* @see Container#isFocusCycleRoot
* @see Container#setFocusTraversalPolicyProvider
* @see Container#isFocusTraversalPolicyProvider
* @see KeyboardFocusManager#setDefaultFocusTraversalPolicy
* @see KeyboardFocusManager#getDefaultFocusTraversalPolicy
* @since 1.4
*/
public abstract class FocusTraversalPolicy {
Returns the Component that should receive the focus after aComponent.
aContainer must be a focus cycle root of aComponent or a focus traversal
policy provider.
Params: - aContainer – a focus cycle root of aComponent or focus traversal
policy provider
- aComponent – a (possibly indirect) child of aContainer, or
aContainer itself
Throws: - IllegalArgumentException – if aContainer is not a focus cycle
root of aComponent or a focus traversal policy provider, or if
either aContainer or aComponent is null
Returns: the Component that should receive the focus after aComponent, or
null if no suitable Component can be found
/**
* Returns the Component that should receive the focus after aComponent.
* aContainer must be a focus cycle root of aComponent or a focus traversal
* policy provider.
*
* @param aContainer a focus cycle root of aComponent or focus traversal
* policy provider
* @param aComponent a (possibly indirect) child of aContainer, or
* aContainer itself
* @return the Component that should receive the focus after aComponent, or
* null if no suitable Component can be found
* @throws IllegalArgumentException if aContainer is not a focus cycle
* root of aComponent or a focus traversal policy provider, or if
* either aContainer or aComponent is null
*/
public abstract Component getComponentAfter(Container aContainer,
Component aComponent);
Returns the Component that should receive the focus before aComponent.
aContainer must be a focus cycle root of aComponent or a focus traversal
policy provider.
Params: - aContainer – a focus cycle root of aComponent or focus traversal
policy provider
- aComponent – a (possibly indirect) child of aContainer, or
aContainer itself
Throws: - IllegalArgumentException – if aContainer is not a focus cycle
root of aComponent or a focus traversal policy provider, or if
either aContainer or aComponent is null
Returns: the Component that should receive the focus before aComponent,
or null if no suitable Component can be found
/**
* Returns the Component that should receive the focus before aComponent.
* aContainer must be a focus cycle root of aComponent or a focus traversal
* policy provider.
*
* @param aContainer a focus cycle root of aComponent or focus traversal
* policy provider
* @param aComponent a (possibly indirect) child of aContainer, or
* aContainer itself
* @return the Component that should receive the focus before aComponent,
* or null if no suitable Component can be found
* @throws IllegalArgumentException if aContainer is not a focus cycle
* root of aComponent or a focus traversal policy provider, or if
* either aContainer or aComponent is null
*/
public abstract Component getComponentBefore(Container aContainer,
Component aComponent);
Returns the first Component in the traversal cycle. This method is used
to determine the next Component to focus when traversal wraps in the
forward direction.
Params: - aContainer – the focus cycle root or focus traversal policy provider
whose first Component is to be returned
Throws: - IllegalArgumentException – if aContainer is null
Returns: the first Component in the traversal cycle of aContainer,
or null if no suitable Component can be found
/**
* Returns the first Component in the traversal cycle. This method is used
* to determine the next Component to focus when traversal wraps in the
* forward direction.
*
* @param aContainer the focus cycle root or focus traversal policy provider
* whose first Component is to be returned
* @return the first Component in the traversal cycle of aContainer,
* or null if no suitable Component can be found
* @throws IllegalArgumentException if aContainer is null
*/
public abstract Component getFirstComponent(Container aContainer);
Returns the last Component in the traversal cycle. This method is used
to determine the next Component to focus when traversal wraps in the
reverse direction.
Params: - aContainer – the focus cycle root or focus traversal policy
provider whose last Component is to be returned
Throws: - IllegalArgumentException – if aContainer is null
Returns: the last Component in the traversal cycle of aContainer,
or null if no suitable Component can be found
/**
* Returns the last Component in the traversal cycle. This method is used
* to determine the next Component to focus when traversal wraps in the
* reverse direction.
*
* @param aContainer the focus cycle root or focus traversal policy
* provider whose last Component is to be returned
* @return the last Component in the traversal cycle of aContainer,
* or null if no suitable Component can be found
* @throws IllegalArgumentException if aContainer is null
*/
public abstract Component getLastComponent(Container aContainer);
Returns the default Component to focus. This Component will be the first
to receive focus when traversing down into a new focus traversal cycle
rooted at aContainer.
Params: - aContainer – the focus cycle root or focus traversal policy
provider whose default Component is to be returned
Throws: - IllegalArgumentException – if aContainer is null
Returns: the default Component in the traversal cycle of aContainer,
or null if no suitable Component can be found
/**
* Returns the default Component to focus. This Component will be the first
* to receive focus when traversing down into a new focus traversal cycle
* rooted at aContainer.
*
* @param aContainer the focus cycle root or focus traversal policy
* provider whose default Component is to be returned
* @return the default Component in the traversal cycle of aContainer,
* or null if no suitable Component can be found
* @throws IllegalArgumentException if aContainer is null
*/
public abstract Component getDefaultComponent(Container aContainer);
Returns the Component that should receive the focus when a Window is made visible for the first time. Once the Window has been made visible by a call to show() or setVisible(true), the initial Component will not be used again. Instead, if the Window loses and subsequently regains focus, or is made invisible or undisplayable and subsequently made visible and displayable, the Window's most recently focused Component will become the focus owner. The default implementation of this method returns the default Component. Params: - window – the Window whose initial Component is to be returned
Throws: - IllegalArgumentException – if window is null
See Also: Returns: the Component that should receive the focus when window is made
visible for the first time, or null if no suitable Component can
be found
/**
* Returns the Component that should receive the focus when a Window is
* made visible for the first time. Once the Window has been made visible
* by a call to {@code show()} or {@code setVisible(true)}, the
* initial Component will not be used again. Instead, if the Window loses
* and subsequently regains focus, or is made invisible or undisplayable
* and subsequently made visible and displayable, the Window's most
* recently focused Component will become the focus owner. The default
* implementation of this method returns the default Component.
*
* @param window the Window whose initial Component is to be returned
* @return the Component that should receive the focus when window is made
* visible for the first time, or null if no suitable Component can
* be found
* @see #getDefaultComponent
* @see Window#getMostRecentFocusOwner
* @throws IllegalArgumentException if window is null
*/
public Component getInitialComponent(Window window) {
if ( window == null ){
throw new IllegalArgumentException("window cannot be equal to null.");
}
Component def = getDefaultComponent(window);
if (def == null && window.isFocusableWindow()) {
def = window;
}
return def;
}
}