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25 
26 package java.util;
27 
28 /**
29  * This exception may be thrown by methods that have detected concurrent
30  * modification of an object when such modification is not permissible.
31  * <p>
32  * For example, it is not generally permissible for one thread to modify a Collection
33  * while another thread is iterating over it.  In general, the results of the
34  * iteration are undefined under these circumstances.  Some Iterator
35  * implementations (including those of all the general purpose collection implementations
36  * provided by the JRE) may choose to throw this exception if this behavior is
37  * detected.  Iterators that do this are known as <i>fail-fast</i> iterators,
38  * as they fail quickly and cleanly, rather that risking arbitrary,
39  * non-deterministic behavior at an undetermined time in the future.
40  * <p>
41  * Note that this exception does not always indicate that an object has
42  * been concurrently modified by a <i>different</i> thread.  If a single
43  * thread issues a sequence of method invocations that violates the
44  * contract of an object, the object may throw this exception.  For
45  * example, if a thread modifies a collection directly while it is
46  * iterating over the collection with a fail-fast iterator, the iterator
47  * will throw this exception.
48  *
49  * <p>Note that fail-fast behavior cannot be guaranteed as it is, generally
50  * speaking, impossible to make any hard guarantees in the presence of
51  * unsynchronized concurrent modification.  Fail-fast operations
52  * throw {@code ConcurrentModificationException} on a best-effort basis.
53  * Therefore, it would be wrong to write a program that depended on this
54  * exception for its correctness: <i>{@code ConcurrentModificationException}
55  * should be used only to detect bugs.</i>
56  *
57  * @author  Josh Bloch
58  * @see     Collection
59  * @see     Iterator
60  * @see     Spliterator
61  * @see     ListIterator
62  * @see     Vector
63  * @see     LinkedList
64  * @see     HashSet
65  * @see     Hashtable
66  * @see     TreeMap
67  * @see     AbstractList
68  * @since   1.2
69  */
70 public class ConcurrentModificationException extends RuntimeException {
71     private static final long serialVersionUID = -3666751008965953603L;
72 
73     /**
74      * Constructs a ConcurrentModificationException with no
75      * detail message.
76      */
ConcurrentModificationException()77     public ConcurrentModificationException() {
78     }
79 
80     /**
81      * Constructs a {@code ConcurrentModificationException} with the
82      * specified detail message.
83      *
84      * @param message the detail message pertaining to this exception.
85      */
ConcurrentModificationException(String message)86     public ConcurrentModificationException(String message) {
87         super(message);
88     }
89 
90     /**
91      * Constructs a new exception with the specified cause and a detail
92      * message of {@code (cause==null ? null : cause.toString())} (which
93      * typically contains the class and detail message of {@code cause}.
94      *
95      * @param  cause the cause (which is saved for later retrieval by the
96      *         {@link Throwable#getCause()} method).  (A {@code null} value is
97      *         permitted, and indicates that the cause is nonexistent or
98      *         unknown.)
99      * @since  1.7
100      */
ConcurrentModificationException(Throwable cause)101     public ConcurrentModificationException(Throwable cause) {
102         super(cause);
103     }
104 
105     /**
106      * Constructs a new exception with the specified detail message and
107      * cause.
108      *
109      * <p>Note that the detail message associated with <code>cause</code> is
110      * <i>not</i> automatically incorporated in this exception's detail
111      * message.
112      *
113      * @param  message the detail message (which is saved for later retrieval
114      *         by the {@link Throwable#getMessage()} method).
115      * @param  cause the cause (which is saved for later retrieval by the
116      *         {@link Throwable#getCause()} method).  (A {@code null} value
117      *         is permitted, and indicates that the cause is nonexistent or
118      *         unknown.)
119      * @since 1.7
120      */
ConcurrentModificationException(String message, Throwable cause)121     public ConcurrentModificationException(String message, Throwable cause) {
122         super(message, cause);
123     }
124 }
125