java - 单例类每次都返回新实例

Question

我正在尝试创建一个单例类，但它每次都会返回一个新实例。这是我的代码。

我有什么错误吗？为什么每次都会返回一个新实例？

我想应该是一样的。

public final class SingletonA {     
    private static SingletonA instance;

    private SingletonA(){
    }

    public static SingletonA getInstance() {    
        if(instance==null)
        {
            System.out.println("RETURNING NEW INSTANCE OF SingletonA Class");
            return new SingletonA();
        }
        System.out.println("RETURNING OLD INSTANCE OF SingletonA Class");
        return instance;
    }
}

public class SingletonB {
    public static void main(String[] args) {
        SingletonA one = SingletonA.getInstance();
        System.out.println("1."+one+" | "+one.hashCode());

        SingletonA two = SingletonA.getInstance();
        System.out.println("2."+two+" | "+two.hashCode());

        SingletonA three = SingletonA.getInstance();
        System.out.println("3."+three+" | "+three.hashCode());
    }
}

// HERE IS THE OUTPUT
RETURNING NEW INSTANCE OF SingletonA Class
1.oop.singleton.SingletonA@2a139a55 | 705927765
RETURNING NEW INSTANCE OF SingletonA Class
2.oop.singleton.SingletonA@15db9742 | 366712642
RETURNING NEW INSTANCE OF SingletonA Class
3.oop.singleton.SingletonA@6d06d69c | 1829164700

Answer 1

如下更改

if(instance==null) {
    System.out.println("RETURNING NEW INSTANCE OF SingletonA Class");
    instance = new SingletonA();
}