1 class Singleton1//饿汉式 2 { 3     private Singleton1(){}//先把构造方法私有化，不允许外界创建对象 4     private static final Singleton1 instance=new Singleton1(); 5     /*饿汉式就是声明的时候就赋值了 6     缺点为加载的时候就需要开辟空间，需要损耗性能，加载慢。 7     */ 8     public static Singleton1 getInstance() 9     {10         return instance;11     }12 }13 class Singleton2//懒汉式14 {15     private Singleton2(){}16     private static Singleton2 instance;//=null17     /*懒汉式就是声明的时候没有赋值18     缺点为线程不安全19     */20     public static Singleton2 getInstance()21     {22         if(instance==null)23             instance=new Singleton2();24         return instance;25     }26 }27 class SingletonDemo 28 {29     public static void main(String[] args) 30     {31         Singleton1 s1=Singleton1.getInstance();32         Singleton1 s2=Singleton1.getInstance();33         System.out.println(s1==s2);34 35         Singleton2 s3=Singleton2.getInstance();36         Singleton2 s4=Singleton2.getInstance();37         System.out.println(s3==s4);38     }39 }