public class

FocusEvent

extends ComponentEvent
java.lang.Object
   ↳ java.util.EventObject
     ↳ java.awt.AWTEvent
       ↳ java.awt.event.ComponentEvent
         ↳ java.awt.event.FocusEvent
Known Direct Subclasses

Class Overview

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.

See Also

Summary

Constants
int FOCUS_FIRST The first number in the range of ids used for focus events.
int FOCUS_GAINED This event indicates that the Component is now the focus owner.
int FOCUS_LAST The last number in the range of ids used for focus events.
int FOCUS_LOST This event indicates that the Component is no longer the focus owner.
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Inherited Constants
From class java.awt.event.ComponentEvent
From class java.awt.AWTEvent
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Inherited Fields
From class java.awt.AWTEvent
From class java.util.EventObject
Public Constructors
FocusEvent(Component source, int id, boolean temporary, Component opposite)
Constructs a FocusEvent object with the specified temporary state and opposite Component.
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)
Constructs a FocusEvent object and identifies it as a permanent change in focus.
Public Methods
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.
[Expand]
Inherited Methods
From class java.awt.event.ComponentEvent
From class java.awt.AWTEvent
From class java.util.EventObject
From class java.lang.Object

Constants

public static final int FOCUS_FIRST

The first number in the range of ids used for focus events.

Constant Value: 1004 (0x000003ec)

public static final int FOCUS_GAINED

This event indicates that the Component is now the focus owner.

Constant Value: 1004 (0x000003ec)

public static final int FOCUS_LAST

The last number in the range of ids used for focus events.

Constant Value: 1005 (0x000003ed)

public static final int FOCUS_LOST

This event indicates that the Component is no longer the focus owner.

Constant Value: 1005 (0x000003ed)

Public Constructors

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

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

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

Public Methods

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

public boolean isTemporary ()

Identifies the focus change event as temporary or permanent.

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

public String paramString ()

Returns a parameter string identifying this event. This method is useful for event-logging and for debugging.

Returns
  • a string identifying the event and its attributes