Class 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.

Every FocusEvent records its cause - the reason why this event was generated. The cause is assigned during the focus event creation and may be retrieved by calling getCause().

An unspecified behavior will be caused if the id parameter of any particular FocusEvent instance is not in the range from FOCUS_FIRST to FOCUS_LAST.

Since:
1.1
See Also:
FocusAdapter, FocusListener, Tutorial: Writing a Focus Listener, Serialized Form

Nested Classes

Modifier and Type Class Description
static class  FocusEvent.Cause

This enum represents the cause of a FocusEvent- the reason why it occurred.

Fields

Modifier and Type Field Description
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 declared in class java.awt.event.ComponentEvent

COMPONENT_FIRST, COMPONENT_HIDDEN, COMPONENT_LAST, COMPONENT_MOVED, COMPONENT_RESIZED, COMPONENT_SHOWN

Fields declared in 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 declared in class java.util.EventObject

source

Constructors

Constructor Description
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, opposite Component and the Cause.UNKNOWN cause.
FocusEvent​(Component source, int id, boolean temporary, Component opposite, FocusEvent.Cause cause)

Constructs a FocusEvent object with the specified temporary state, opposite Component and the cause.

Methods

Modifier and Type Method Description
FocusEvent.Cause getCause()

Returns the event cause.
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 declared in class java.awt.event.ComponentEvent

getComponent

Methods declared in class java.awt.AWTEvent

consume, getID, isConsumed, setSource, toString

Methods declared in class java.util.EventObject

getSource

Methods declared in class java.lang.Object

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

Fields

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

Constructors

FocusEvent

public FocusEvent(Component source,
                  int id,
                  boolean temporary,
                  Component opposite)

Constructs a FocusEvent object with the specified temporary state, opposite Component and the Cause.UNKNOWN cause. 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.

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. For information on allowable values, see the class description for FocusEvent
temporary - Equals true if the focus change is temporary; false otherwise
opposite - The other Component involved in the focus change, or null
Throws:
IllegalArgumentException - if source equals null
Since:
1.4
See Also:
EventObject.getSource(), AWTEvent.getID(), isTemporary(), getOppositeComponent(), FocusEvent.Cause.UNKNOWN

FocusEvent

public FocusEvent(Component source,
                  int id,
                  boolean temporary,
                  Component opposite,
                  FocusEvent.Cause cause)

Constructs a FocusEvent object with the specified temporary state, opposite Component and the cause. 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.

This method throws an IllegalArgumentException if source or cause is null.

Parameters:
source - The Component that originated the event
id - An integer indicating the type of event. For information on allowable values, see the class description for FocusEvent
temporary - Equals true if the focus change is temporary; false otherwise
opposite - The other Component involved in the focus change, or null
cause - The focus event cause.
Throws:
IllegalArgumentException - if source equals null or if cause equals null
Since:
9
See Also:
EventObject.getSource(), AWTEvent.getID(), isTemporary(), getOppositeComponent(), FocusEvent.Cause

FocusEvent

public FocusEvent(Component source,
                  int id,
                  boolean temporary)

Constructs a FocusEvent object and identifies whether or not the change is temporary.

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. For information on allowable values, see the class description for FocusEvent
temporary - Equals true if the focus change is temporary; false otherwise
Throws:
IllegalArgumentException - if source equals null
See Also:
EventObject.getSource(), AWTEvent.getID(), isTemporary()

FocusEvent

public FocusEvent(Component source,
                  int id)

Constructs a FocusEvent object and identifies it as a permanent change in focus.

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. For information on allowable values, see the class description for FocusEvent
Throws:
IllegalArgumentException - if source equals null
See Also:
EventObject.getSource(), AWTEvent.getID()

Methods

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

getCause

public final FocusEvent.Cause getCause()

Returns the event cause.

Returns:
one of FocusEvent.Cause values
Since:
9

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https://docs.oracle.com/en/java/javase/11/docs/api/java.desktop/java/awt/event/FocusEvent.html