如何以正确的方式写一个单身人士？

问题描述

今天在采访中，一位采访者要求我写一个Singleton课。我给了我答案

Today in my interview one interviewer asked me to write a Singleton class. And i gave my answer as

public class Singleton {

    private static Singleton ref;

    private Singleton() {
    }

    public static Singleton getInstance() {
        if (ref == null) {
            ref = new Singleton();
        }
        return ref;
    }
}

突然他告诉我这是旧的写作方式类。任何一个请帮助我，为什么他这样说。

suddenly he told me this is old way of writing the class. Can any one please help me why he told like that.

推荐答案

创建单例时我想到的第一件事是枚举。我通常使用枚举来实现单例：

The first thing which comes to my mind when creating a singleton is enum. I generally use enum to implement singleton:

enum Singleton {
    INSTANCE;
}

使用枚举获得的一个好处是使用序列化。

One benefit you get with using enum is with Serialization.

使用单例类，您必须确保序列化和反序列化不会通过实现 readResolve（）方法，而枚举不是这样。

With singleton class, you would have to make sure that serialization and deserialization doesn't create a new instance by implementing the readResolve() method, while this is not the case with enum.

使用类，您应该像这样创建单例：

Using class you should create the singleton like this:

public final class Singleton implements Serializable {
    // For lazy-laoding (if only you want)
    private static class SingletonHolder {
        private static final Singleton INSTANCE = new Singleton();
    }

    private Singleton() {
        if (SingletonHolder.INSTANCE != null) {
            // throw Some Exception
        }
    }

    public static Singleton getInstance() {
        return SingletonHolder.INSTANCE;
    }

    // To avoid deserialization create new instance
    @SuppressWarnings("unused")
    private Singleton readResolve() {
        return SingletonHolder.INSTANCE;
    }
}

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