使用枚举方式实现单例模式

public class Singleton7 {
    public static void main(String[] args) {
        Singleton singleton1 = Singleton.INSTANCE;
        Singleton singleton2 = Singleton.INSTANCE;
        System.out.println(singleton1 == singleton2);


        System.out.println(singleton1.hashCode());
        System.out.println(singleton2.hashCode());

        singleton1.add();
    }
}

enum Singleton {
    INSTANCE;

    public void add() {
        System.out.println("我是枚举");
    }
}