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 * published by the Free Software Foundation.  Oracle designates this

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 * by Oracle in the LICENSE file that accompanied this code.

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 * This code is distributed in the hope that it will be useful, but WITHOUT

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 * 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

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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="http://java.sun.com/docs/books/tutorial/post1.0/ui/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();

    }

}