使用单例设计模式时，其他方法是否需要使用synced关键字来确保线程安全？ [英] When using the singleton design pattern, do other methods need to use synchronized keyword to ensure thread safety?

问题描述

我想确保以下类是线程安全的，是否应将synced关键字用于其他方法？或使用线程安全的数据结构存储电子邮件。我该怎么办？

I want to ensure that the following class is thread-safe, should I use the synchronized keyword for other methods? Or use a thread-safe data structure to store Email. What should I do?

public class RecycleStation {
    private static volatile RecycleStation uniqueInstance;
    private static List<Email> recycleEmailList ;

    private RecycleStation() {
        recycleEmailList = new ArrayList<>();
    }

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

    public void RecycleEmail(Email email) {
        recycleEmailList.add(email);
    }

    public void deleteEmail(Email email) {
        recycleEmailList.remove(email);
    }

    public void clear() {
        recycleEmailList.clear();
    }

}

推荐答案

首先，最好将Singleton模式实现为Java中的Enum
其次，每个电子邮件操作功能（清除，回收，删除）应同步以确保线程安全（该链接是一个枚举，但是每个Sinlgeton实现都相同）：

First, a Singleton pattern is best implemented as Enum in Java Second, each email manipulation function (clear, Recycle, delete) should be synchronized to ensure thread safety (the link is about an Enum, but the same holds about each and every Sinlgeton implementation):

public synchronized void RecycleEmail(Email email)

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