JavaTM 2 Platform
Standard Ed. 5.0

java.awt.event
Class FocusEvent

java.lang.Object
  extended by java.util.EventObject
      extended by java.awt.AWTEvent
          extended by java.awt.event.ComponentEvent
              extended by java.awt.event.FocusEvent
All Implemented Interfaces:
Serializable

public class FocusEvent
extends ComponentEvent

A low-level event which indicates that a Component has gained or lost the input focus. This low-level event is generated by a Component (such as a TextField). The event is passed to every FocusListener or FocusAdapter object which registered to receive such events using the Component's addFocusListener method. ( FocusAdapter objects implement the FocusListener interface.) Each such listener object gets this FocusEvent when the event occurs.

There are two levels of focus events: permanent and temporary. Permanent focus change events occur when focus is directly moved from one Component to another, such as through a call to requestFocus() or as the user uses the TAB key to traverse Components. Temporary focus change events occur when focus is temporarily lost for a Component as the indirect result of another operation, such as Window deactivation or a Scrollbar drag. In this case, the original focus state will automatically be restored once that operation is finished, or, for the case of Window deactivation, when the Window is reactivated. Both permanent and temporary focus events are delivered using the FOCUS_GAINED and FOCUS_LOST event ids; the level may be distinguished in the event using the isTemporary() method.

Since:
1.1
See Also:
FocusAdapter, FocusListener, Tutorial: Writing a Focus Listener, Reference: The Java Class Libraries (update file), Serialized Form

Field Summary
static int FOCUS_FIRST
          The first number in the range of ids used for focus events.
static int FOCUS_GAINED
          This event indicates that the Component is now the focus owner.
static int FOCUS_LAST
          The last number in the range of ids used for focus events.
static int FOCUS_LOST
          This event indicates that the Component is no longer the focus owner.
 
Fields inherited from class java.awt.event.ComponentEvent
COMPONENT_FIRST, COMPONENT_HIDDEN, COMPONENT_LAST, COMPONENT_MOVED, COMPONENT_RESIZED, COMPONENT_SHOWN
 
Fields inherited from class java.awt.AWTEvent
ACTION_EVENT_MASK, ADJUSTMENT_EVENT_MASK, COMPONENT_EVENT_MASK, consumed, CONTAINER_EVENT_MASK, FOCUS_EVENT_MASK, HIERARCHY_BOUNDS_EVENT_MASK, HIERARCHY_EVENT_MASK, id, INPUT_METHOD_EVENT_MASK, INVOCATION_EVENT_MASK, ITEM_EVENT_MASK, KEY_EVENT_MASK, MOUSE_EVENT_MASK, MOUSE_MOTION_EVENT_MASK, MOUSE_WHEEL_EVENT_MASK, PAINT_EVENT_MASK, RESERVED_ID_MAX, TEXT_EVENT_MASK, WINDOW_EVENT_MASK, WINDOW_FOCUS_EVENT_MASK, WINDOW_STATE_EVENT_MASK
 
Fields inherited from class java.util.EventObject
source
 
Constructor Summary
FocusEvent(Component source, int id)
          Constructs a FocusEvent object and identifies it as a permanent change in focus.
FocusEvent(Component source, int id, boolean temporary)
          Constructs a FocusEvent object and identifies whether or not the change is temporary.
FocusEvent(Component source, int id, boolean temporary, Component opposite)
          Constructs a FocusEvent object with the specified temporary state and opposite Component.
 
Method Summary
 Component getOppositeComponent()
          Returns the other Component involved in this focus change.
 boolean isTemporary()
          Identifies the focus change event as temporary or permanent.
 String paramString()
          Returns a parameter string identifying this event.
 
Methods inherited from class java.awt.event.ComponentEvent
getComponent
 
Methods inherited from class java.awt.AWTEvent
consume, getID, isConsumed, setSource, toString
 
Methods inherited from class java.util.EventObject
getSource
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

FOCUS_FIRST

public static final int FOCUS_FIRST
The first number in the range of ids used for focus events.

See Also:
Constant Field Values

FOCUS_LAST

public static final int FOCUS_LAST
The last number in the range of ids used for focus events.

See Also:
Constant Field Values

FOCUS_GAINED

public static final int FOCUS_GAINED
This event indicates that the Component is now the focus owner.

See Also:
Constant Field Values

FOCUS_LOST

public static final int FOCUS_LOST
This event indicates that the Component is no longer the focus owner.

See Also:
Constant Field Values
Constructor Detail

FocusEvent

public FocusEvent(Component source,
                  int id,
                  boolean temporary,
                  Component opposite)
Constructs a FocusEvent object with the specified temporary state and opposite Component. The opposite Component is the other Component involved in this focus change. For a FOCUS_GAINED event, this is the Component that lost focus. For a FOCUS_LOST event, this is the Component that gained focus. If this focus change occurs with a native application, with a Java application in a different VM, or with no other Component, then the opposite Component is null.

Note that passing in an invalid id results in unspecified behavior. This method throws an IllegalArgumentException if source is null.

Parameters:
source - the Component that originated the event
id - FOCUS_GAINED or FOCUS_LOST
temporary - true if the focus change is temporary; false otherwise
opposite - the other Component involved in the focus change, or null
Throws:
IllegalArgumentException - if source is null

FocusEvent

public FocusEvent(Component source,
                  int id,
                  boolean temporary)
Constructs a FocusEvent object and identifies whether or not the change is temporary.

Note that passing in an invalid id results in unspecified behavior. This method throws an IllegalArgumentException if source is null.

Parameters:
source - the Component that originated the event
id - an integer indicating the type of event
temporary - true if the focus change is temporary; false otherwise
Throws:
IllegalArgumentException - if source is null

FocusEvent

public FocusEvent(Component source,
                  int id)
Constructs a FocusEvent object and identifies it as a permanent change in focus.

Note that passing in an invalid id results in unspecified behavior. This method throws an IllegalArgumentException if source is null.

Parameters:
source - the Component that originated the event
id - an integer indicating the type of event
Throws:
IllegalArgumentException - if source is null
Method Detail

isTemporary

public boolean isTemporary()
Identifies the focus change event as temporary or permanent.

Returns:
true if the focus change is temporary; false otherwise

getOppositeComponent

public Component getOppositeComponent()
Returns the other Component involved in this focus change. For a FOCUS_GAINED event, this is the Component that lost focus. For a FOCUS_LOST event, this is the Component that gained focus. If this focus change occurs with a native application, with a Java application in a different VM or context, or with no other Component, then null is returned.

Returns:
the other Component involved in the focus change, or null
Since:
1.4

paramString

public String paramString()
Returns a parameter string identifying this event. This method is useful for event-logging and for debugging.

Overrides:
paramString in class ComponentEvent
Returns:
a string identifying the event and its attributes

JavaTM 2 Platform
Standard Ed. 5.0

Submit a bug or feature
For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2004 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.


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