单例模式之内部静态类

public class Singleton
{
    private Singleton(){ }

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

    //在第一次被引用时被加载
    static class Nested
    {
        private static Singleton instance = new Singleton();
    }

    public static void main(String args[])
    {
        Singleton instance = Singleton.getInstance();
        Singleton instance2 = Singleton.getInstance();
        System.out.println(instance == instance2);
    }
}