本篇是在学习5.Thread和Object中线程相关的重要方法 (ycyin.eu.org)时对
notify()和wait()的相关用法记录。
方法一：使用同步锁
public class PrintNumberWithTwoThread {
private static final Object lock = new Object();
private static int i = 0;
public static void main(String[] args) throws InterruptedException {
Thread1 thread1 = new Thread1();
Thread2 thread2 = new Thread2();
thread1.start();
thread2.start();
}
static class Thread1 extends Thread {
@Override
public void run() {
while (i < 100) {
synchronized (lock) {
if ((i & 1) == 1) {
System.out.println("线程" + Thread.currentThread().getName() + ":" + i++);
}
}
// 打印出来就会发现进行了多次无效的循环
// System.out.println("进入循环");
}
}
}
static class Thread2 extends Thread {
@Override
public void run() {
while (i < 100) {
synchronized (lock) {
if ((i & 1) == 0) {
System.out.println("线程" + Thread.currentThread().getName() + ":" + i++);
}
}
// System.out.println("进入循环");
}
}
}
}
使用这种方法效率较低，会多次进入循环争夺锁。比如Thread2如果一直持有lock就会一直循环下去，变量不增加循环就不会结束，一直到另一个线程Thread1争夺到lock锁，以此反复，最终变量i自增到100,两个线程都结束循环，程序结束。
方法二：使用notify()和wait()
public class PrintNumberWithTwoThread2 {
private static final Object lock = new Object();
private static int i = 0;
public static void main(String[] args) throws InterruptedException {
Target target = new Target();
Thread thread1 = new Thread(target,"偶数");
Thread thread2 = new Thread(target,"奇数");
thread1.start();
// 先让偶数线程启动
Thread.sleep(100);
thread2.start();
}
static class Target implements Runnable{
@Override
public void run() {
while (i <= 100) {
synchronized (lock) {
System.out.println("线程" + Thread.currentThread().getName() + ":" + i++);
lock.notify();
if (i <= 100) {
try {
lock.wait();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
}
}
}
使用这种方式比方法一要好得多。线程启动后获取到lock锁，开始打印数据，打印后调用notify()通知另一个线程，本线程因为调用wait()方法进入"Waiting"状态并释放锁，另一个线程获取锁，打印数据，调用notify()通知另一个线程，以此反复完成变量i自增到100结束线程。