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add order_print_num.md in codeinterview.
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‎codeinterview/order_print_num.md‎

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问题分析：首先我们需要看清楚题目，多线程、顺序打印、然后就是几个线程交替顺序打印；
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首先看下输出结果：
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```
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thread-0:0
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thread-1:1
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thread-2:2
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```
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其实这个题目的重点就是怎么实现多个线程交替顺序打印，想一想，这里我们需要用到的就是线程间的通信，然后怎么通信呢？
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我们可以通过 synchronized + wait + notifyAll，或者 ReentrantLock + Condition + await + signalAll；
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知道了线程间怎么通信，然后就是在每个线程内部怎么实现了，是不是多个线程共用一把锁，然后自然数0-100是公共资源，让3个线程去消费；
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我们可以每个线程加上一个标号：0，1，2，来表示具体是哪个线程；
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通过一个计数器对3进行求余，余数和具体的线程标号去比较，只有当余数和线程标号相等的时候才进行打印(不等加入等待队列)，打印完计数器进行自增；
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然后唤醒等待队列里面线程去获取锁，获取锁成功则继续执行以上步骤，否则加入锁的同步队列中，等待上一个线程唤醒；
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`用 synchronized 锁实现如下：`
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```java
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class PrintThread1 implements Runnable {
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private static final Object LOCK = new Object();
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private static int count = 0; // 计数，同时确定线程是否要加入等待队列，还是可以直接去资源队列里面去获取数据进行打印
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private LinkedList<Integer> queue;
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private Integer threadNo;
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public PrintThread1(LinkedList<Integer> queue, Integer threadNo) {
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this.queue = queue;
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this.threadNo = threadNo;
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}
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@Override
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public void run() {
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while (true) {
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synchronized (LOCK) {
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while (count % 3 != this.threadNo) {
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if (count >= 101) {
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break;
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}
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try {
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LOCK.wait();
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} catch (InterruptedException e) {
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e.printStackTrace();
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}
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}
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if (count >= 101) {
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break;
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}
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Integer val = this.queue.poll();
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System.out.println("thread-" + this.threadNo + ":" + val);
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count++;
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LOCK.notifyAll();
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}
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}
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}
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}
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```
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`用 ReentrantLock 锁实现如下：`
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```java
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class PrintThread2 implements Runnable {
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private static final ReentrantLock lock = new ReentrantLock();
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private static final Condition c = lock.newCondition();
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private static int count = 0; //作为计数，同时也作为资源；因为这道题目是自然数作为资源，所以正好可以公用；
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private Integer threadNo;
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public PrintThread2(Integer threadNo) {
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this.threadNo = threadNo;
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}
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@Override
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public void run() {
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while (true) {
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try {
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lock.lock();
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while (count % 3 != this.threadNo) {
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if (count >= 101) {
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break;
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}
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try {
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c.await();
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} catch (InterruptedException e) {
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e.printStackTrace();
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}
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}
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if (count >= 101) {
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break;
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}
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System.out.println("thread-" + this.threadNo + ":" + count);
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count++;
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c.signalAll();
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} finally {
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lock.unlock();
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}
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}
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}
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}
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```
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`具体代码实现：`
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参见：[code](https://github.com/joyang1/JavaInterview/blob/master/codeinterview/src/main/java/cn/tommyyang/multithread/OrderPrintNum.java)

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