package testthread;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/*
* 编写一个程序，开启3个线程，这3个线程的ID分别为A、B、C，每个线程将自己的ID在屏幕上打印10遍，
* 要求输出结果必须按ABC的顺序显示；如：ABCABC….依次递推。
*
* 使用condition接口、lock类、ReentrantLock类实现线程的通信
*
*/
public class TestLock {
public static void main(String[] args) {
final AlternateDemo ad = new AlternateDemo(); //在使用Java局部内部类或者匿名内部类时，若该类调用了所在方法的局部变量，则该局部变量必须使用final关键字来修饰，否则将会出现编译错误“Cannot refer to a non-final variable * inside an inner class defined in a different method”
new Thread(new Runnable() {
@Override
public void run() {
for (int i = 0; i < 10; i++) {
ad.loopA();
}
}
}, "A").start();
new Thread(new Runnable() {
@Override
public void run() {
for (int i = 0; i < 10; i++) {
ad.loopB();
}
}
}, "B").start();
new Thread(new Runnable() {
@Override
public void run() {
for (int i = 0; i < 10; i++) {
ad.loopC();
System.out.println("-----------------------------------");
}
}
}, "C").start();
}
}
class AlternateDemo {
private int number = 1; //当前正在执行线程的标记
private Lock lock = new ReentrantLock();
private Condition condition1 = lock.newCondition();
private Condition condition2 = lock.newCondition();
private Condition condition3 = lock.newCondition();
public void loopA() {
lock.lock();//类比去银行办理业务，此行代码相当于先拿到一个办理业务的排队号码
try {
//1. 判断
if (number != 1) {
condition1.await();//线程等待之后，该线程中的其它代码都不会被执行，就直接退出了
}
//2. 打印
System.out.println(Thread.currentThread().getName());
//3. 唤醒
number = 2;
condition2.signal();//尝试去唤醒一个其它等待的满足条件的线程，每个线程都会拿到一次锁，若条件满足将会执行该线程，否则将会等待
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void loopB() {
lock.lock();
try {
//1. 判断
if (number != 2) {
condition2.await();//等待之后将会释放锁
}
//2. 打印
System.out.println(Thread.currentThread().getName());
//3. 唤醒
number = 3;
condition3.signal();
//condition3.toString();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void loopC() {
lock.lock();
try {
//1. 判断
if (number != 3) {
condition3.await();
}
//2. 打印
System.out.println(Thread.currentThread().getName());
//3. 唤醒
number = 1;
condition1.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}