java - 同步类的成员变量

Question

我正在学习线程。在学习的过程中，我遇到了一个场景，其中两个线程使用一个静态变量。

我想要两个线程之间的同步行为。

这是我的代码:

package com.learning.fizzbuzz;

public class Trigger {

    public static void main(String[] args) {

        Solution s = new Solution("thread1");
        s.start(20);

        Solution s1 = new Solution("thread2");
        s1.start(15);

    }

}

package com.learning.fizzbuzz;

import java.util.ArrayList;
import java.util.List;

public class Solution implements Runnable{

    private Thread t;

    private String threadName;

    private static int n;

    public Solution(String threadName) {
        this.threadName = threadName;
        System.out.println("Creating thread :: "+ threadName);
    }

    public static List<String> fizzBuzz(int n) {

        List<String> elements = new ArrayList<>();

        for (int i = 1; i <= n; i++) {
            if (i % (15) == 0) {
                elements.add("FizzBuzz");
            }
            else if (i % 3 == 0) {
                elements.add("Fizz");
            }
            else if (i % 5 == 0) {
                elements.add("Buzz");
            }
            else {
                elements.add(String.valueOf(i));
            }
        }

        return elements;
    }

    public static String reverseString(String s) {
        StringBuffer str = new StringBuffer(s);
        s = str.reverse().toString();
        return s;
    }

    @Override
    public synchronized void run() {
            System.out.println("Executing thread :: " + threadName);
            List<String> str = fizzBuzz(n);
            System.out.println(str +" :: "+ t.getName());
            System.out.println(reverseString("Hello") +" :: "+ t.getName());
    }

    public void start(int num) {
        if (t == null) {
            System.out.println("Starting thread :: " + threadName);
            t = new Thread(this, threadName);
            Solution.n = num;
            System.out.println("number is " + n);
            t.start();
        } else {
            System.out.println("Thread Already Created and Running :: " + threadName);
        }
    }
}

我尝试同步解决方案类的各个块，但无法获得如下所述的结果。

[1, 2, Fizz, 4, Buzz, Fizz, 7, 8, Fizz, Buzz, 11, Fizz, 13, 14, FizzBuzz, 16, 17, Fizz, 19, Buzz] :: thread2 olleH :: thread2

[1, 2, Fizz, 4, Buzz, Fizz, 7, 8, Fizz, Buzz, 11, Fizz, 13, 14, FizzBuzz] :: thread1 olleH :: thread1

请指教。

编辑:我观察到的一件事是，在两个线程开始执行之前，n的值设置为15。如何避免呢？

Answer 1

要访问静态共享变量，您需要在同一监视器上同步两个(或多个)线程。

在方法实例上使用关键字synchronized不能完成此操作，因为它在变量this上同步。

最简单的方法是使用静态变量进行同步。

public class MyClass {
    private static Object lock = new Object();

    private static int sharedVariable;

    public void yourMethod() {

        synchronized(lock) {
           // Do something with sharedVariable
        }
    }

}