其实此题是模拟多用户对相同资源的操作。网上大多解法只是解决了基本的同步问题，并未解决对于资源的控制。

• 可使用lock condition条件对象及await() signalALL()来解决问题。

package com.javalearn;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class Resources {
    private int data;
    private Lock lock;
    private Condition lastData;

    public Resources() {
        this.data = 0;
        this.lock = new ReentrantLock();
        this.lastData = lock.newCondition();
    }

    public void dec() throws InterruptedException {
        lock.lock();
        try {
            while (this.data==0)
                lastData.await();
            this.data--;
            System.out.println(Thread.currentThread()+" "+this.data);
            lastData.signalAll();
        } finally {
            lock.unlock();
        }
    }
    public void inc() throws InterruptedException {
        lock.lock();
        try {
            while (this.data==1)
                lastData.await();
            this.data++;
            System.out.println(Thread.currentThread()+" "+this.data);
            lastData.signalAll();
        } finally {
            lock.unlock();
        }
    }
    public static void main(String[] args) {
        Resources res = new Resources();
        for (int i = 0; i < 100; i++) {
            new Thread(()->{
                for (int j = 0; j < 100; j++) {
                    try {
                        res.dec();
                        Thread.sleep(15);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"decrement"+i).start();
        }
        for (int i = 0; i < 10; i++) {
            new Thread(()->{
                for (int j = 0; j < 1000; j++) {
                    try {
                        res.inc();
                        Thread.sleep(10);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"increment"+i).start();
        }
    }
}

• 可使用synchronized及wait()和notifyALL()来解决。

package com.javalearn;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class Resources {
    private int data = 0;
    public synchronized void dec() throws InterruptedException {
        while (this.data==0)
            wait();
        this.data--;
        System.out.println(Thread.currentThread()+" "+this.data);
        notifyAll();
    }
    public synchronized void inc() throws InterruptedException {
        while (this.data==1)
            wait();
        this.data++;
        System.out.println(Thread.currentThread()+" "+this.data);
        notifyAll();
    }
    public static void main(String[] args) {
        Resources res = new Resources();
        for (int i = 0; i < 100; i++) {//此处设置加法线程数量
            new Thread(()->{
                for (int j = 0; j < 100; j++) {
                    try {
                        res.dec();
                        Thread.sleep(15);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"decrement"+i).start();
        }
        for (int i = 0; i < 10; i++) {//此处设置减法线程数量
            new Thread(()->{
                for (int j = 0; j < 1000; j++) {
                    try {
                        res.inc();
                        Thread.sleep(10);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            },"increment"+i).start();
        }
    }
}

两种代码都是比较标准的模板，可以参考使用。建议使用较为简洁的第二种类。l