曾经有面试官问过这样一个问题，如何让两个线程交替打印奇数和偶数？如何让多个线程交替执行？
回答这个问题之前需要先了解java多线程的运行机制，线程间通信机制，线程同步问题。
这个问题我知道的实现方案有两种，一种是基于synchronized和wait/notify，另外一种是基于Lock和Condition.
1.基于synchronized和wait/notify
public class ChangeABC {
private Object lock = new Object();
private boolean RUN0 = true;
private static final int LIMIT = 10;
public static void main(String[] args) throws InterruptedException {
final ChangeABC o = new ChangeABC();
new Thread(new Runnable() {
@Override
public void run() {
try {
o.m0();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "t0").start();
new Thread(new Runnable() {
@Override
public void run() {
try {
o.m1();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "t1").start();
Thread.sleep(10 * 1000);
}private void m1() throws InterruptedException {
for (int i = 1;
i < LIMIT;
i += 2) {
synchronized (lock) {
if (RUN0) {
lock.wait();
}
System.out.println(Thread.currentThread().getName() + "___" + i);
RUN0 = true;
lock.notify();
}
}
}private void m0() throws InterruptedException {
for (int i = 0;
i < LIMIT;
i += 2) {
synchronized (lock) {
if (!RUN0) {
lock.wait();
}
System.out.println(Thread.currentThread().getName() + "___" + i);
RUN0 = false;
lock.notify();
}
}
}
}2.基于Lock和Condition
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/*** 线程间通信-基于lock的condition* @date 2017年12月21日*/
public class ChangeABC1 {
private Lock lock = new ReentrantLock();
private Condition c0 = lock.newCondition();
private Condition c1 = lock.newCondition();
private Condition c2 = lock.newCondition();
private int status = 0;
private static final int LIMIT = 10;
public static void main(String[] args) throws InterruptedException {
ExecutorService exec = new ThreadPoolExecutor(3, 30, 60, TimeUnit.SECONDS, new LinkedBlockingQueue(300), Executors.defaultThreadFactory(), new ThreadPoolExecutor.AbortPolicy());
final ChangeABC1 o = new ChangeABC1();
exec.submit(o.createTask(0));
exec.submit(o.createTask(1));
exec.submit(o.createTask(2));
exec.shutdown();
exec.awaitTermination(5, TimeUnit.MINUTES);
}/*** @param name* @param i*/
private Runnable createTask(final int i) {
return new Runnable() {
@Override
public void run() {
try {
m(i);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
};
}private void m(final int n) throws InterruptedException {
for (int i = n;
i < LIMIT;
i += 3) {
lock.lock();
try {
switch (n) {
case 0:
if (status != 0) {
c0.await();
}
System.out.println(Thread.currentThread().getName() + "___" + i);
status = 1;
c1.signal();
break;
case 1:
if (status != 1) {
c1.await();
}
System.out.println(Thread.currentThread().getName() + "___" + i);
status = 2;
c2.signal();
break;
case 2:
if (status != 2) {
c2.await();
}
System.out.println(Thread.currentThread().getName() + "___" + i);
status = 0;
c0.signal();
break;
default:
break;
}
} finally {
lock.unlock();
}
}
}
}【多线程练习（三）三个线程交互打印】链接：https://www.jianshu.com/p/dcc66a6f37cb
