单例模式总结

即时加载

public class Singleton {
	private static final Singleton uniqueInstance = new Singleton();

	private Singleton() {
	}

	public static Singleton getInstance() {
		return uniqueInstance;
	}
}

注意volatile关键字

public class Singleton {
	private volatile static Singleton uniqueInstance;

	private Singleton() {
	}

	public static Singleton getInstance() {
		if (uniqueInstance == null) {
			synchronized (Singleton.class) {
				if (uniqueInstance == null) {
					uniqueInstance = new Singleton();
				}
			}
		}
		return uniqueInstance;
	}
}

内部静态类在第一次被引用时加载，是线程安全的

public class Singleton {
	private Singleton() {
	}

	public static Singleton getInstance() {
		return Nested.uniqueInstance;
	}

	static class Nested {
		private static final Singleton uniqueInstance = new Singleton();
	}
}

注意实现readResolve方法，并且所用带有对象引用的实例域都必须声明为transient，详见《Effective Java》第77条。

import java.io.Serializable;

public class Singleton implements Serializable {
	private static final Singleton uniqueInstance = new Singleton();

	private transient String element = "singleton";

	private Singleton() {
	}

	public static Singleton getInstance() {
		return uniqueInstance;
	}

	private Object readResolve() {
		return uniqueInstance;
	}
}

单例的最佳实现方法，提供序列化机制，防止多次实例化，并且线程安全。

public enum Singleton {
	INSTANCE;

	// elements & methods
}

单例模式总结

原文：http://blog.csdn.net/perfect8886/article/details/39394101