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Java java.awt.event Class FocusEvent（JDK8）

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Java™ Platform
Standard Ed. 8
java.awt.event

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.

    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

    • 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.

        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

        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()

    • 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
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Java™ Platform
Standard Ed. 8

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