java.awt
Class FocusTraversalPolicy

java.lang.Object
  java.awt.FocusTraversalPolicy

Direct Known Subclasses:

ContainerOrderFocusTraversalPolicy, InternalFrameFocusTraversalPolicy, LegacyGlueFocusTraversalPolicy

public abstract class FocusTraversalPolicy

extends Object

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.

Since:

1.4

Author:

David Mendenhall

See Also:

Container.setFocusTraversalPolicy(java.awt.FocusTraversalPolicy), Container.getFocusTraversalPolicy(), KeyboardFocusManager.setDefaultFocusTraversalPolicy(java.awt.FocusTraversalPolicy), KeyboardFocusManager.getDefaultFocusTraversalPolicy()

Constructor Summary

FocusTraversalPolicy()

Method Summary

abstract Component	getComponentAfter(Container focusCycleRoot, Component aComponent) Returns the Component that should receive the focus after aComponent.
abstract Component	getComponentBefore(Container focusCycleRoot, Component aComponent) Returns the Component that should receive the focus before aComponent.
abstract Component	getDefaultComponent(Container focusCycleRoot) Returns the default Component to focus.
abstract Component	getFirstComponent(Container focusCycleRoot) Returns the first Component in the traversal cycle.
Component	getInitialComponent(Window window) Returns the Component that should receive the focus when a Window is made visible for the first time.
abstract Component	getLastComponent(Container focusCycleRoot) Returns the last Component in the traversal cycle.

Methods inherited from class java.lang.Object

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

Constructor Detail

FocusTraversalPolicy

public FocusTraversalPolicy()

Method Detail

getComponentAfter

public abstract Component getComponentAfter(Container focusCycleRoot,
                                            Component aComponent)

Returns the Component that should receive the focus after aComponent. focusCycleRoot must be a focus cycle root of aComponent.

Parameters:

focusCycleRoot - a focus cycle root of aComponent

aComponent - a (possibly indirect) child of focusCycleRoot, or focusCycleRoot itself

Returns:

the Component that should receive the focus after aComponent, or null if no suitable Component can be found

Throws:

IllegalArgumentException - if focusCycleRoot is not a focus cycle root of aComponent, or if either focusCycleRoot or aComponent is null

getComponentBefore

public abstract Component getComponentBefore(Container focusCycleRoot,
                                             Component aComponent)

Returns the Component that should receive the focus before aComponent. focusCycleRoot must be a focus cycle root of aComponent.

Parameters:

focusCycleRoot - a focus cycle root of aComponent

aComponent - a (possibly indirect) child of focusCycleRoot, or focusCycleRoot itself

Returns:

the Component that should receive the focus before aComponent, or null if no suitable Component can be found

Throws:

IllegalArgumentException - if focusCycleRoot is not a focus cycle root of aComponent, or if either focusCycleRoot or aComponent is null

getFirstComponent

public abstract Component getFirstComponent(Container focusCycleRoot)

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.

Parameters:

focusCycleRoot - the focus cycle root whose first Component is to be returned

Returns:

the first Component in the traversal cycle when focusCycleRoot is the focus cycle root, or null if no suitable Component can be found

Throws:

IllegalArgumentException - if focusCycleRoot is null

getLastComponent

public abstract Component getLastComponent(Container focusCycleRoot)

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.

Parameters:

focusCycleRoot - the focus cycle root whose last Component is to be returned

Returns:

the last Component in the traversal cycle when focusCycleRoot is the focus cycle root, or null if no suitable Component can be found

Throws:

IllegalArgumentException - if focusCycleRoot is null

getDefaultComponent

public abstract Component getDefaultComponent(Container focusCycleRoot)

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 focusCycleRoot.

Parameters:

focusCycleRoot - the focus cycle root whose default Component is to be returned

Returns:

the default Component in the traversal cycle when focusCycleRoot is the focus cycle root, or null if no suitable Component can be found

Throws:

IllegalArgumentException - if focusCycleRoot is null

getInitialComponent

public Component getInitialComponent(Window window)

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.

Parameters:

window - the Window whose initial Component is to be returned

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

Throws:

IllegalArgumentException - if window is null

See Also:

getDefaultComponent(java.awt.Container), Window.getMostRecentFocusOwner()