私有静态内部类实现线程安全的单例

public class Singleton
{
	//构造器私有化
	private Singleton(){ }
	
	/**
	 * 获取对象实例的静态方法
	 * @return
	 */
	public static Singleton getInstance()
	{
		return SingletonHolder.instance;		
	}
	
	//静态内部类，在第一次被引用时被加载
	private static class SingletonHolder
	{
		private static Singleton instance = new Singleton();
	}
	
	public static void main(String args[])
	{
		Singleton instance1 = Singleton.getInstance();
		Singleton instance2 = Singleton.getInstance();
		System.out.println(instance1 == instance2);
		
		
	}
}