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FocusEvent (Java 2 Platform SE 5.0) - JDK 5 Documentation v1.5.0, Java 2 SDK 英文文档

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java.awt.event
Class FocusEvent

java.lang.Object
  java.util.EventObject
      java.awt.AWTEvent
          java.awt.event.ComponentEvent
              java.awt.event.FocusEvent

All Implemented Interfaces:

Serializable

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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

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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

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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

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FOCUS_GAINED

public static final int FOCUS_GAINED

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

See Also:

Constant Field Values

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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

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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

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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

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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

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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

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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.

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