Java多线程题目

本文转载自ethanzhou的51CTO博客
题目如下:
四个线程a,b,c,d. 线程a,b对变量i加一. 线程c,d对变量i减去一.四个线程顺序执行, 每个线程每次只执行一次.i的初始值为0， 打印结果0 1 2 1 0 1 2 1 0 1 2…

package demo;

import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;

/**
 * 四个线程a,b,c,d. 线程a,b对变量i加一.
 * 线程c,d对变量i减去一.四个线程顺序执行,
 * 每个线程每次只执行一次.i的初始值为0，
 * 打印结果0 1 2 1 0 1 2 1 0 1 2...
 *
 */
public class Demo02 {

    private int i = 0;

    private BlockingQueue queue = new LinkedBlockingQueue<>();

    public Demo02() {
        queue.offer(1);
        queue.offer(2);
        queue.offer(3);
        queue.offer(4);
    }

    public synchronized void plus(int condition) throws InterruptedException{
        while(true){
            int c = queue.peek();
            if (c==condition) {
                break;
            }else {
                notifyAll();
                wait();
            }
        }
        queue.offer(queue.take());
        i++;
        System.out.println(Thread.currentThread().getName()+",i="+i);
    }

    public synchronized void subtract(int condition) throws InterruptedException{
        while(true){
            int c = queue.peek();
            if (c==condition) {
                break;
            }else {
                notifyAll();
                wait();
            }
        }
        queue.offer(queue.take());
        i--;
        System.out.println(Thread.currentThread().getName()+",i="+i);
    }

    private  class plusThread implements Runnable{
        // 条件
        private int condition;

        public plusThread(int condition) {
            this.condition = condition;
        }

        @Override
        public void run() {
            while (true){
                try {
                    plus(condition);
                } catch (InterruptedException e) {
                    System.err.println(Thread.currentThread().getName() + " exit now");
                    break;
                }
            }
        }
    }

    private class subtractThread implements Runnable{
        private int condition;

        public subtractThread(int condition) {
            this.condition = condition;
        }

        @Override
        public void run() {
            while (true){
                try {
                    subtract(condition);
                } catch (InterruptedException e) {
                    System.err.println(Thread.currentThread().getName() + " exit now");
                    break;
                }
            }
        }
    }

    public static void main(String[] args) {
        Demo02 demo02 = new Demo02();
        ExecutorService exec = Executors.newFixedThreadPool(4);
        exec.submit(demo02. new plusThread(1));
        exec.submit(demo02.new plusThread(2));
        exec.submit(demo02. new subtractThread(3));
        exec.submit(demo02.new subtractThread(4));
        exec.shutdown();
    }

}

这段代码顺便让我温顾了线程池，BlockingQueue类的一些方法，对于链式的LinkedBlockingQueue也有了更形象的认识，固转载记录一下。