Java多线程入门(三) H2O

题目：  实现两个函数: H() and O(), 这两个函数会被多线程调用。当一个线程调用H或O时，如果当前已经有至少两个线程call H和一个线程call O。那么让两个call H和一个 call O的线程返回（产生一个水分子），其他的都block。

package multiThreads;

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

class H2O {
    int Hcount;
    int Ocount;
    Lock lock = new ReentrantLock();
    Condition cH = lock.newCondition();
    Condition cO = lock.newCondition();
 
    public void H() {
        lock.lock();
        Hcount++;
        if (Hcount >= 2 && Ocount >= 1) {
            Hcount -= 2;
            Ocount -= 1;
            cH.signal();
            cO.signal();
            System.out.println("H2O");
        } else {
            try {
                cH.await();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        lock.unlock();
    }
 
    public void O() {
        lock.lock();
        Ocount++;
        if (Hcount >= 2 && Ocount >= 1) {
            Hcount -= 2;
            Ocount -= 1;
            cH.signal();
            cH.signal();
            System.out.println("H2O");
        } else {
            try {
                cO.await();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        lock.unlock();
    }
}

class Hclass implements Runnable {
    private H2O obj;
 
    public Hclass(H2O obj) {
        this.obj = obj;
    }
    @Override
    public void run() {
        // TODO Auto-generated method stub
        obj.H();
    }
 
}

class Oclass implements Runnable {
    private H2O obj;
 
    public Oclass(H2O obj) {
        this.obj = obj;
    }
    @Override
    public void run() {
        // TODO Auto-generated method stub
        obj.O();
    }
 
}

public class H2Oexample {
    final private static H2O obj = new H2O();
 
    public static void main(String[] args) {
        for (int i = 0; i< 10; i++) {
            new Thread(new Hclass(obj)).start();
        }
        for (int i = 0; i< 5; i++) {
            new Thread(new Oclass(obj)).start();
        }
    }
}