ComponentEvent


1   /*
2    * @(#)ComponentEvent.java  1.27 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.awt.event;
9   
10  import java.awt.AWTEvent  ;
11  import java.awt.Event  ;
12  import java.awt.Component  ;
13  import java.awt.Rectangle  ;
14  
15  /**
16   * A low-level event which indicates that a component moved, changed
17   * size, or changed visibility (also, the root class for the other 
18   * component-level events).
19   * <P>
20   * Component events are provided for notification purposes ONLY;
21   * The AWT will automatically handle component moves and resizes
22   * internally so that GUI layout works properly regardless of
23   * whether a program is receiving these events or not.
24   * <P>
25   * In addition to serving as the base class for other component-related
26   * events (InputEvent, FocusEvent, WindowEvent, ContainerEvent),
27   * this class defines the events that indicate changes in
28   * a component's size, position, or visibility. 
29   * <P>
30   * This low-level event is generated by a component object (such as a 
31   * List) when the component is moved, resized, rendered invisible, or made
32   * visible again. The event is passed to every <code>ComponentListener</code>
33   * or <code>ComponentAdapter</code> object which registered to receive such
34   * events using the component's <code>addComponentListener</code> method.
35   * (<code>ComponentAdapter</code> objects implement the 
36   * <code>ComponentListener</code> interface.) Each such listener object 
37   * gets this <code>ComponentEvent</code> when the event occurs.
38   *
39   * @see ComponentAdapter
40   * @see ComponentListener
41   * @see <a HREF="http://java.sun.com/docs/books/tutorial/post1.0/ui/componentlistener.html">Tutorial: Writing a Component Listener</a>
42   * @see <a HREF="http://www.awl.com/cp/javaseries/jcl1_2.html">Reference: The Java Class Libraries (update file)</a>
43   *
44   * @author Carl Quinn
45   * @version 1.27 12/19/03
46   * @since 1.1
47   */
48  public class ComponentEvent extends AWTEvent   {
49  
50      /**
51       * The first number in the range of ids used for component events.
52       */
53      public static final int COMPONENT_FIRST     = 100;
54  
55      /**
56       * The last number in the range of ids used for component events.
57       */
58      public static final int COMPONENT_LAST      = 103;
59  
60     /**
61       * This event indicates that the component's position changed.
62       */
63      public static final int COMPONENT_MOVED = COMPONENT_FIRST;
64  
65      /**
66       * This event indicates that the component's size changed.
67       */
68      public static final int COMPONENT_RESIZED   = 1 + COMPONENT_FIRST;
69  
70      /**
71       * This event indicates that the component was made visible.
72       */
73      public static final int COMPONENT_SHOWN = 2 + COMPONENT_FIRST;
74  
75      /**
76       * This event indicates that the component was rendered invisible.
77       */
78      public static final int COMPONENT_HIDDEN    = 3 + COMPONENT_FIRST;
79  
80      /*
81       * JDK 1.1 serialVersionUID 
82       */
83      private static final long serialVersionUID = 8101406823902992965L;
84  
85      /**
86       * Constructs a <code>ComponentEvent</code> object.
87       * <p>Note that passing in an invalid <code>id</code> results in
88       * unspecified behavior. This method throws an
89       * <code>IllegalArgumentException</code> if <code>source</code>
90       * is <code>null</code>.
91       *
92       * @param source the <code>Component</code> that originated the event
93       * @param id     an integer indicating the type of event
94       * @throws IllegalArgumentException if <code>source</code> is null
95       */
96      public ComponentEvent(Component   source, int id) {
97          super(source, id);
98      }
99  
100     /**
101      * Returns the originator of the event.
102      *
103      * @return the <code>Component</code> object that originated 
104      * the event, or <code>null</code> if the object is not a 
105      * <code>Component</code>.  
106      */
107     public Component   getComponent() {
108         return (source instanceof Component  ) ? (Component  )source : null;
109     }
110 
111     /**
112      * Returns a parameter string identifying this event.
113      * This method is useful for event-logging and for debugging.
114      *
115      * @return a string identifying the event and its attributes
116      */
117     public String   paramString() {
118         String   typeStr;
119         Rectangle   b = (source !=null
120                ? ((Component  )source).getBounds()
121                : null);
122 
123         switch(id) {
124           case COMPONENT_SHOWN:
125               typeStr = "COMPONENT_SHOWN";
126               break;
127           case COMPONENT_HIDDEN:
128               typeStr = "COMPONENT_HIDDEN";
129               break;
130           case COMPONENT_MOVED:
131               typeStr = "COMPONENT_MOVED ("+ 
132                          b.x+","+b.y+" "+b.width+"x"+b.height+")";
133               break;
134           case COMPONENT_RESIZED:
135               typeStr = "COMPONENT_RESIZED ("+ 
136                          b.x+","+b.y+" "+b.width+"x"+b.height+")";
137               break;
138           default:
139               typeStr = "unknown type";
140         }
141         return typeStr;
142     }
143 }
144
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