单例模式

单例模式之 饿汉式

public class Singleton {
    private final static Singleton s= new Singleton();
    private Singleton() {}
    public static Singleton getInstance() {
        return s;
    }
}

单例模式之 懒汉式

public class SingletonLazy {
    private static SingletonLazy s = null;
    private SingletonLazy() {}
    public static SingletonLazy getInstance() {
        if(s==null) {
            s= new SingletonLazy();
        }
        return s;
    }
}

public class TestSingleton {
    public static void main(String[] args) {
        Singleton s = Singleton.getInstance();
        Singleton s2 =Singleton.getInstance();
        Singleton s3 = Singleton.getInstance();
        System.out.println(s ==s2);
        System.out.println(s ==s3);
        System.out.println(s.equals(s3));
        
        SingletonLazy sl1 = SingletonLazy.getInstance();
        SingletonLazy sl2 = SingletonLazy.getInstance();
        System.out.println(sl1 == sl2);
    }
}