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Showing content from https://docs.oracle.com/en/java/javase/19/docs/api/java.desktop/java/awt/event/FocusEvent.html below:

FocusEvent (Java SE 19 & JDK 19)

All Implemented Interfaces:

Serializable

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

or

object which registered to receive such events using the Component's

method. (

objects implement the

interface.) Each such listener object gets this

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 Class Summary

  Nested Classes

  static enum 

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

• Field Summary

  Fields

  static final int

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

  static final int

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

  static final int

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

  static final int

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

  Fields declared in class java.awt.AWTEventACTION_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
• Constructor Summary

  Constructors

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

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

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

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

• Method Summary

  Returns the other Component involved in this focus change.

  boolean

  Identifies the focus change event as temporary or permanent.

  Returns a parameter string identifying this event.

• Field Details
  • 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 Details
  • FocusEvent

    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

    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

    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()

• Method Details
  • isTemporary

    public boolean isTemporary()

    Identifies the focus change event as temporary or permanent.

    Returns:

    true if the focus change is temporary; false otherwise

  • 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

    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

    Returns the event cause.

    Returns:

    one of FocusEvent.Cause values

    Since:

    9

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