建立三个线程A、B、C，A线程打印10次字母A，B线程打印10次字母B,C线程打印10次字母C，但是要求三个线程同时运行，并且实现交替打印，即按照ABCABCABC的顺序打印。
考察多线程类的实际应用
思路 选择使用ReentrantLock 维护一个公有变量，每次打印的时候使用一个Lock锁住，打印完成之后解锁。
package com.ncst.collections;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @author i
* @create 2020/7/11 16:32
* @Description
*/
public class ThreeThreadPrint {
private static Lock lock = new ReentrantLock();
private static int state = 0;//通过state的值来确定是哪个线程打印
static class ThreadA implements Runnable {
@Override
public void run() {
for (int i = 0; i < 10 ; ) {
try {
lock.lock();
while(state%3==0){//多线程并发，不能用if 必须用循环测试等待条件，避免虚假唤醒
System.out.print("A->");
state++;
i++;
}
}catch (Exception e){
e.printStackTrace();
}finally {
lock.unlock();
}
}
}
}
static class ThreadB implements Runnable {
@Override
public void run() {
for (int i = 0; i < 10 ; ) {
try {
lock.lock();
while(state%3==1){
System.out.print("B->");
state++;
i++;
}
}catch (Exception e){
e.printStackTrace();
}finally {
lock.unlock();
}
}
}
}
static class ThreadC implements Runnable {
@Override
public void run() {
for (int i = 0; i < 10 ; ) {
try {
lock.lock();
while(state%3==2){
System.out.print("C->");
state++;
i++;
}
}catch (Exception e){
e.printStackTrace();
}finally {
lock.unlock();
}
}
}
}
public static void main(String[] args) {
new Thread(new ThreadA()).start();
new Thread(new ThreadB()).start();
new Thread(new ThreadC()).start();
}
}
