java - 线程中的私有(private)成员从另一个线程更改

Question

我的第一个问题。 Java 自学成才，非专家。

我有一个主应用程序创建一个管理器线程。管理器将创建工作线程。 Main 会将“Properties”作为参数传递给 Manager。 Manager 会对属性进行一些添加，并将其作为参数传递给每个 Worker。

问题:

在实例化辅助对象后，当我更改属于管理器的属性成员时，属于辅助线程的属性成员也会发生变化.由于 Worker 类中的属性是私有(private)成员，我认为它只能在 Worker 类中更改。为什么当我在管理器中进行更改时它会发生变化？我怎样才能避免这个问题？

这里附上一个简单版本的代码:

主.java:

import java.util.Properties;

public class Main {
    public static void main(String arg[])
    {
        Properties properties = new Properties();
        properties.put("p1", "v1");
        Manager manager = new Manager(properties);
        manager.start();
    }
}

管理器.java:

import java.util.Properties;

public class Manager {
    private Properties properties;

    Manager(Properties argProperties)
    {
        properties = argProperties;
    }

    public void start()
    {
        properties.put("workerId", "worker1");
        spawnWorker();

        try {
            Thread.sleep(2000);
        }catch(InterruptedException ex){
            //do nothing
        }

        System.out.println("Manager going to change worker ID to 2");
        properties.put("workerId", "worker2");
        spawnWorker();

        try {
            Thread.sleep(2000);
        }catch(InterruptedException ex){
            //do nothing
        }

        Thread manager = new Thread("manager"){
            public void run() {
                System.out.println("Manager going to change worker ID to haha");
                while(true)
                {
                    try {
                        properties.put("workerId", "hahaha");
                        Thread.sleep(1000);
                    }catch(InterruptedException ex){
                        //do nothing
                    }
                }
            }
        };
        manager.start();
    }

    private void spawnWorker()
    {
        Worker worker = new Worker(properties);
        worker.start();
    }
}

worker .java:

import java.util.Properties;

public class Worker {
    private final Properties properties;
    String workerId;

    Worker(Properties argProperties)
    {
        properties = argProperties;
        workerId = properties.getProperty("workerId");
    }

    public void start()
    {
        Thread worker = new Thread("worker-" + workerId){
            public void run() {
                while(true)
                {
                    try {
                        System.out.println(this.getName() + "<->" + properties.getProperty("workerId"));
                        Thread.sleep(1000);
                    }catch(InterruptedException ex){
                        //do nothing
                    }
                }
            }
        };
        worker.start();
    }
}

输出:

worker-worker1<->worker1
worker-worker1<->worker1
worker-worker1<->worker1
Manager going to change worker ID to 2
worker-worker2<->worker2
worker-worker1<->worker2
worker-worker2<->worker2
worker-worker1<->worker2
Manager going to change worker ID to haha
worker-worker2<->worker2
worker-worker1<->hahaha
worker-worker2<->hahaha

Answer 1

您正在将相同的 Properties 实例传递给每个 worker。因此每个 worker 都可以改变它的内容。

在生成新工作人员之前，您应该复制属性并将此副本传递给工作人员。

//更多背景:变量修饰符用于声明变量的可见性。不能从外部类访问私有(private)成员。但它可以通过引用(正如您所做的那样，通过构造函数传递引用)或公共(public) getter 公开。因此，可以更改公开的私有(private)成员内容。

可以在这里找到详细信息:

• https://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html

和

• Is Java "pass-by-reference" or "pass-by-value"?