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/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/licenses/publicdomain
*/
package edu.emory.mathcs.backport.java.util.concurrent.atomic;
/**
* An object reference that may be updated atomically. See the {@link
* edu.emory.mathcs.backport.java.util.concurrent.atomic} package specification for description
* of the properties of atomic variables.
* @since 1.5
* @author Doug Lea
*/
public class AtomicReference implements java.io.Serializable {
private static final long serialVersionUID = -1848883965231344442L;
private volatile Object value;
/**
* Creates a new AtomicReference with the given initial value.
*
* @param initialValue the initial value
*/
public AtomicReference(Object initialValue) {
value = initialValue;
}
/**
* Creates a new AtomicReference with null initial value.
*/
public AtomicReference() {
}
/**
* Gets the current value.
*
* @return the current value
*/
public final Object get() {
return value;
}
/**
* Sets to the given value.
*
* @param newValue the new value
*/
public final synchronized void set(Object newValue) {
value = newValue;
}
/**
* Eventually sets to the given value.
*
* @param newValue the new value
* @since 1.6
*/
public final synchronized void lazySet(Object newValue) {
value = newValue;
}
/**
* Atomically sets the value to the given updated value
* if the current value {@code ==} the expected value.
* @param expect the expected value
* @param update the new value
* @return true if successful. False return indicates that
* the actual value was not equal to the expected value.
*/
public final synchronized boolean compareAndSet(Object expect, Object update) {
if (value == expect) {
value = update;
return true;
}
return false;
}
/**
* Atomically sets the value to the given updated value
* if the current value {@code ==} the expected value.
*
* May fail spuriously
* and does not provide ordering guarantees, so is only rarely an
* appropriate alternative to {@code compareAndSet}.
*
* @param expect the expected value
* @param update the new value
* @return true if successful.
*/
public final synchronized boolean weakCompareAndSet(Object expect, Object update) {
if (value == expect) {
value = update;
return true;
}
return false;
}
/**
* Atomically sets to the given value and returns the old value.
*
* @param newValue the new value
* @return the previous value
*/
public final synchronized Object getAndSet(Object newValue) {
Object old = value;
value = newValue;
return old;
}
/**
* Returns the String representation of the current value.
* @return the String representation of the current value.
*/
public String toString() {
return String.valueOf(get());
}
}