Back to index...

	/*
	* Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.awt.event;

	import java.awt.Component;
	import sun.awt.AppContext;
	import sun.awt.SunToolkit;

	/**
	* 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 <code>FocusListener</code> or
	* <code>FocusAdapter</code> object which registered to receive such events
	* using the Component's <code>addFocusListener</code> method. (<code>
	* FocusAdapter</code> objects implement the <code>FocusListener</code>
	* interface.) Each such listener object gets this <code>FocusEvent</code> when
	* the event occurs.
	* <p>
	* 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.
	* <p>
	* An unspecified behavior will be caused if the {@code id} parameter
	* of any particular {@code FocusEvent} instance is not
	* in the range from {@code FOCUS_FIRST} to {@code FOCUS_LAST}.
	*
	* @see FocusAdapter
	* @see FocusListener
	* @see <a href="https://docs.oracle.com/javase/tutorial/uiswing/events/focuslistener.html">Tutorial: Writing a Focus Listener</a>
	*
	* @author Carl Quinn
	* @author Amy Fowler
	* @since 1.1
	*/
	public class FocusEvent extends ComponentEvent {

	/**
	* The first number in the range of ids used for focus events.
	*/
	public static final int FOCUS_FIRST = 1004;

	/**
	* The last number in the range of ids used for focus events.
	*/
	public static final int FOCUS_LAST = 1005;

	/**
	* This event indicates that the Component is now the focus owner.
	*/
	public static final int FOCUS_GAINED = FOCUS_FIRST; //Event.GOT_FOCUS

	/**
	* This event indicates that the Component is no longer the focus owner.
	*/
	public static final int FOCUS_LOST = 1 + FOCUS_FIRST; //Event.LOST_FOCUS

	/**
	* A focus event can have two different levels, permanent and temporary.
	* It will be set to true if some operation takes away the focus
	* temporarily and intends on getting it back once the event is completed.
	* Otherwise it will be set to false.
	*
	* @serial
	* @see #isTemporary
	*/
	boolean temporary;

	/**
	* 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, a Java application in a different VM, or with
	* no other Component, then the opposite Component is null.
	*
	* @see #getOppositeComponent
	* @since 1.4
	*/
	transient Component opposite;

	/*
	* JDK 1.1 serialVersionUID
	*/
	private static final long serialVersionUID = 523753786457416396L;

	/**
	* Constructs a <code>FocusEvent</code> object with the
	* specified temporary state and opposite <code>Component</code>.
	* The opposite <code>Component</code> is the other
	* <code>Component</code> involved in this focus change.
	* For a <code>FOCUS_GAINED</code> event, this is the
	* <code>Component</code> that lost focus. For a
	* <code>FOCUS_LOST</code> event, this is the <code>Component</code>
	* that gained focus. If this focus change occurs with a native
	* application, with a Java application in a different VM,
	* or with no other <code>Component</code>, then the opposite
	* <code>Component</code> is <code>null</code>.
	* <p> This method throws an
	* <code>IllegalArgumentException</code> if <code>source</code>
	* is <code>null</code>.
	*
	* @param source The <code>Component</code> that originated the event
	* @param id An integer indicating the type of event.
	* For information on allowable values, see
	* the class description for {@link FocusEvent}
	* @param temporary Equals <code>true</code> if the focus change is temporary;
	* <code>false</code> otherwise
	* @param opposite The other Component involved in the focus change,
	* or <code>null</code>
	* @throws IllegalArgumentException if <code>source</code> equals {@code null}
	* @see #getSource()
	* @see #getID()
	* @see #isTemporary()
	* @see #getOppositeComponent()
	* @since 1.4
	*/
	public FocusEvent(Component source, int id, boolean temporary,
	Component opposite) {
	super(source, id);
	this.temporary = temporary;
	this.opposite = opposite;
	}

	/**
	* Constructs a <code>FocusEvent</code> object and identifies
	* whether or not the change is temporary.
	* <p> This method throws an
	* <code>IllegalArgumentException</code> if <code>source</code>
	* is <code>null</code>.
	*
	* @param source The <code>Component</code> that originated the event
	* @param id An integer indicating the type of event.
	* For information on allowable values, see
	* the class description for {@link FocusEvent}
	* @param temporary Equals <code>true</code> if the focus change is temporary;
	* <code>false</code> otherwise
	* @throws IllegalArgumentException if <code>source</code> equals {@code null}
	* @see #getSource()
	* @see #getID()
	* @see #isTemporary()
	*/
	public FocusEvent(Component source, int id, boolean temporary) {
	this(source, id, temporary, null);
	}

	/**
	* Constructs a <code>FocusEvent</code> object and identifies it
	* as a permanent change in focus.
	* <p> This method throws an
	* <code>IllegalArgumentException</code> if <code>source</code>
	* is <code>null</code>.
	*
	* @param source The <code>Component</code> that originated the event
	* @param id An integer indicating the type of event.
	* For information on allowable values, see
	* the class description for {@link FocusEvent}
	* @throws IllegalArgumentException if <code>source</code> equals {@code null}
	* @see #getSource()
	* @see #getID()
	*/
	public FocusEvent(Component source, int id) {
	this(source, id, false);
	}

	/**
	* Identifies the focus change event as temporary or permanent.
	*
	* @return <code>true</code> if the focus change is temporary;
	* <code>false</code> otherwise
	*/
	public boolean isTemporary() {
	return temporary;
	}

	/**
	* 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.
	*
	* @return the other Component involved in the focus change, or null
	* @since 1.4
	*/
	public Component getOppositeComponent() {
	if (opposite == null) {
	return null;
	}

	return (SunToolkit.targetToAppContext(opposite) ==
	AppContext.getAppContext())
	? opposite
	: null;
	}

	/**
	* Returns a parameter string identifying this event.
	* This method is useful for event-logging and for debugging.
	*
	* @return a string identifying the event and its attributes
	*/
	public String paramString() {
	String typeStr;
	switch(id) {
	case FOCUS_GAINED:
	typeStr = "FOCUS_GAINED";
	break;
	case FOCUS_LOST:
	typeStr = "FOCUS_LOST";
	break;
	default:
	typeStr = "unknown type";
	}
	return typeStr + (temporary ? ",temporary" : ",permanent") +
	",opposite=" + getOppositeComponent();
	}

	}

Back to index...