来源：http://melin.iteye.com/blog/838258
三种Singleton的实现方式，一种是用大家熟悉的DCL，另外两种使用cas特性来实现。
public class LazySingleton {
private static volatile LazySingleton instance;
public static LazySingleton getInstantce() {
if (instance == null) {
synchronized (LazySingleton.class) {
if (instance == null) {
instance = new LazySingleton();
}
}
}
return instance;
}
}
/**
* 利用putIfAbsent线程安全操作，实现单例模式
*
* @author Administrator
*
*/
public class ConcurrentSingleton {
private static final ConcurrentMap<String, ConcurrentSingleton> map = new ConcurrentHashMap<String, ConcurrentSingleton>();
private static volatile ConcurrentSingleton instance; public static ConcurrentSingleton getInstance() {
if (instance == null) {
instance = map.putIfAbsent("INSTANCE", new ConcurrentSingleton());
}
return instance;
}
}
public class AtomicBooleanSingleton {
private static AtomicBoolean initialized = new AtomicBoolean(false);
private static volatile AtomicBooleanSingleton instance;
public static AtomicBooleanSingleton getInstantce() {
checkInitialized();
return instance;
}
private static void checkInitialized() {
if(instance == null && initialized.compareAndSet(false, true)) {
instance = new AtomicBooleanSingleton();
}
}
}