Java多线程Lock的使用

最近在看面试题，看到了一个问题，这里记一下想出来的解决方法：
问题：

利用多线程打印：A12B23C34D45E56F67G78H89I910J1011K1112L1213M1314N1415O1516P1617Q1718R1819S1920T2021U2122V2223W2324X2425Y2526Z

想了一下，决定用Lock来实现，下面是实现方法：

先导包：

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

将需要的方法放在一个类里，方便加锁：

public class MyService {

	private ReentrantLock lock=new ReentrantLock();
	private Condition condition = lock.newCondition();
	private boolean flag=false;
	 int i=0;
	
	String[] str= {"A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"};
	public void set() {
		try {
			for (; i < str.length;) {
				lock.lock();
				if(flag==true) {
					condition.await();
				}
				System.out.print(str[i]);
				flag=true;
				i++;
				condition.signal();
			}
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally {
			lock.unlock();
		}
	}
	
	
	public void get() {
		try {
			for (; i < str.length;) {
				lock.lock();
				if(flag==false ) {
					condition.await();
				}
				System.out.print(i);
				System.out.print(i+1);
				flag=false;
				condition.signal();
			}
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}finally {
			lock.unlock();
		}
	}
}

再写两个多线程类：

public class MyThreadA extends Thread{

	private MyService service;

	public MyThreadA(MyService service) {
		super();
		this.service = service;
	}

	@Override
	public void run() {
			service.set();
	}
	
}

public class MyThreadB extends Thread{

	private MyService service;

	public MyThreadB(MyService service) {
		super();
		this.service = service;
	}

	@Override
	public void run() {
			service.get();
	}
	
	
}

然后测试：

	public static void main(String[] args) {
		MyService myService = new MyService();

        MyThreadA a = new MyThreadA(myService);
        MyThreadB b = new MyThreadB(myService);
        
        a.start();

        b.start();
	}

最终结果：

另外还可以使用CyclicBarrier也可以有这种效果（底层也是使用Lock）：

import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.BrokenBarrierException;

代码

public class CyclicTest {

	String[] str= {"A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"};
	CyclicBarrier ccb=new CyclicBarrier(1, new myAction());
	int i=0;
			
	class myAction implements Runnable{
		@Override
		public void run() {
			if(i<=str.length-1) {
				System.out.print(i);
				System.out.print(i+1);
			}
		}
		
	}
}

class ThreadA implements Runnable {

	
	
	private CyclicTest cct;
	
	
	public ThreadA(CyclicTest cct) {
		super();
		this.cct = cct;
	}

	@Override
	public void run() {
		for (; cct.i < cct.str.length;) {
			try {
				System.out.print(cct.str[cct.i]);
				cct.i++;
				cct.ccb.await();
			} catch (InterruptedException | BrokenBarrierException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

}

最后测试方法：

	public static void main(String[] args) {
		CyclicTest cct =new CyclicTest();
		new Thread(new ThreadA(cct)).start();
	}