Java设计模式-单例模式-懒汉式-双重检查

public class SingletonTest06 {
    public static void main(String[] args) {
        Singleton06 instance  = Singleton06.getInstance();
        Singleton06 instance01 = Singleton06.getInstance();

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

class Singleton06 {

    private static volatile Singleton06 singleton;

    private Singleton06() {
    }

    public static Singleton06 getInstance() {
        if (singleton == null) {
            synchronized (Singleton06.class) {
                if (singleton == null) {
                    singleton = new Singleton06();
                }
            }
        }
        return singleton;
    }
}

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