concurrentmodificationexception.java

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package org.garret.perst;

/**
 * This exception may be thrown by methods that have detected concurrent
 * modification of an object when such modification is not permissible.
 * <p>
 * For example, it is not generally permssible for one thread to modify a Collection
 * while another thread is iterating over it.  In general, the results of the
 * iteration are undefined under these circumstances.  Some Iterator
 * implementations (including those of all the collection implementations
 * provided by the JRE) may choose to throw this exception if this behavior is
 * detected.  Iterators that do this are known as <i>fail-fast</i> iterators,
 * as they fail quickly and cleanly, rather that risking arbitrary,
 * non-deterministic behavior at an undetermined time in the future.
 * <p>
 * Note that this exception does not always indicate that an object has
 * been concurrently modified by a <i>different</i> thread.  If a single
 * thread issues a sequence of method invocations that violates the
 * contract of an object, the object may throw this exception.  For
 * example, if a thread modifies a collection directly while it is
 * iterating over the collection with a fail-fast iterator, the iterator
 * will thow this exception.
 *
 * <p>Note that fail-fast behavior cannot be guaranteed as it is, generally
 * speaking, impossible to make any hard guarantees in the presence of
 * unsynchronized concurrent modification.  Fail-fast operations
 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. 
 * Therefore, it would be wrong to write a program that depended on this
 * exception for its correctness: <i><tt>ConcurrentModificationException</tt>
 * should be used only to detect bugs.</i>
 */

public class ConcurrentModificationException extends RuntimeException {
    /**
     * Constructs a ConcurrentModificationException with no
     * detail message.
     */
    public ConcurrentModificationException() {
    }

    /**
     * Constructs a <tt>ConcurrentModificationException</tt> with the
     * specified detail message.
     *
     * @param message the detail message pertaining to this exception.
     */
    public ConcurrentModificationException(String message) {
	super(message);
    }
}