编写一个多线程程序，输出的结果为：1010101010..._两个线程输出10101010-优快云博客

本文展示了如何使用 Java 实现一个多线程程序，其中包含一个对象，其成员变量counter作为计数器。程序创建了四个线程，两个线程增加计数器，两个线程减少计数器，并通过`synchronized`关键字确保线程安全。每个线程在操作后打印counter的值，最终输出序列为1010101010...。这个例子演示了Java中的线程同步和并发控制。

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编写一个多线程程序，实现这样一个目标：
①存在一个对象，该对象有一个int类型的成员变量counter，该成员变量的初始值为0.
②创建四个线程，其中两个线程对该对象的成员变量counter加1，另外两个线程对该对象的成员变量减1.
③输出该对象成员变量counter每次变化后的值。
④最终输出的结果为：1010101010...

public class MyObject {
    private int counter;
    public synchronized void increase() {
        while (counter == 1) {
            try {
                wait();
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
        }
        counter++;
        System.out.println(counter);
        notify();
    }

    public synchronized void decrease() {
        while (counter == 0) {
            try {
                wait();
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
        }
        counter--;
        System.out.println(counter);

        notify();
    }
}

public class DecreaseThread extends Thread {
    private MyObject myObject;
    public DecreaseThread(MyObject myObject) {
        this.myObject = myObject;
    }
    @Override
    public void run() {
        for (int i = 0; i < 10; ++i) {
            try {
                Thread.sleep((long)(Math.random() * 1000));
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
            myObject.decrease();
        }
    }
}

public class IncreaseThread extends Thread {
    private MyObject myObject;
    public IncreaseThread(MyObject myObject) {
        this.myObject = myObject;
    }
    @Override
    public void run() {
        for (int i = 0; i < 30; ++i) {
            try {
                Thread.sleep((long)(Math.random() * 1000));
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
            myObject.increase();
        }
    }
}

public class Client {
    public static void main(String[] args) {
        MyObject myObject = new MyObject();
        Thread increaseThread = new IncreaseThread(myObject);
        Thread increaseThread2 = new IncreaseThread(myObject);
        Thread decreaseThread = new DecreaseThread(myObject);
        Thread decreaseThread2 = new DecreaseThread(myObject);
        increaseThread.start();
        increaseThread2.start();
        decreaseThread.start();
        decreaseThread2.start();
    }
}