Singleton

package cn.xidian.Design.Patterns;

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

package cn.xidian.Design.Patterns;

public class Singleton {
	private static class SingletonInstance {
		private static final Singleton instance = new Singleton();
	}
	public static Singleton getInstance() {
		return SingletonInstance.instance;
	}
	private Singleton() {
	}
}

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Singleton

原文：http://hcx2013.iteye.com/blog/2215665