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25 
26 package java.util;
27 
28 /**
29  * <p>
30  * The root class from which all event state objects shall be derived.
31  * <p>
32  * All Events are constructed with a reference to the object, the "source",
33  * that is logically deemed to be the object upon which the Event in question
34  * initially occurred upon.
35  *
36  * @since 1.1
37  */
38 
39 public class EventObject implements java.io.Serializable {
40 
41     @java.io.Serial
42     private static final long serialVersionUID = 5516075349620653480L;
43 
44     /**
45      * The object on which the Event initially occurred.
46      */
47     protected transient Object source;
48 
49     /**
50      * Constructs a prototypical Event.
51      *
52      * @param source the object on which the Event initially occurred
53      * @throws IllegalArgumentException if source is null
54      */
EventObject(Object source)55     public EventObject(Object source) {
56         if (source == null)
57             throw new IllegalArgumentException("null source");
58 
59         this.source = source;
60     }
61 
62     /**
63      * The object on which the Event initially occurred.
64      *
65      * @return the object on which the Event initially occurred
66      */
getSource()67     public Object getSource() {
68         return source;
69     }
70 
71     /**
72      * Returns a String representation of this EventObject.
73      *
74      * @return a String representation of this EventObject
75      */
toString()76     public String toString() {
77         return getClass().getName() + "[source=" + source + "]";
78     }
79 }
80