Java设计模式-单例模式-饿汉式（静态代码块）

public class SingletonTest04 {
    public static void main(String[] args) {
        Singleton04 instance  = Singleton04.getInstance();
        Singleton04 instance01 = Singleton04.getInstance();

        System.out.println(instance == instance01);
        System.out.println("instance,hashCode = " + instance.hashCode());
        System.out.println("instance01,hashCode = " + instance01.hashCode());
    }
}

class Singleton04 {
    private Singleton04() {}
    private final static Singleton04 instance;
    static {
        instance = new Singleton04();
    }
    public static Singleton04 getInstance(){
        return instance;
    }
}

// 运行结果
true
instance,hashCode = 1846274136
instance01,hashCode = 1846274136