Java n个线程轮流打印数字的问题
2024-08-31 08:58:39
一. 实现两个线程。轮流打印出数字。例如以下：
bThread --> 10
aThread --> 9
bThread --> 8
aThread --> 7
bThread --> 6
aThread --> 5
bThread --> 4
aThread --> 3
bThread --> 2
aThread --> 1
用java中的Lock类实现：
package com.yjq.thread_demo; import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock; public class TwoThreadPrinter { private Lock threadLock = new ReentrantLock(); private boolean flag = false; int count =10; Thread aThread = new Thread(new Runnable() {
public void run() {
while (true) {
// 锁定
threadLock.lock();
try {
if ( count < 1) {
return;
}
if (flag) {
// aThread的任务
System.out.println("aThread --> " + (count--));
flag = !flag;
}
} catch (Exception e) {
// TODO: handle exception
} finally {
// 释放锁
threadLock.unlock();
}
}
}
}); Thread bThread = new Thread(new Runnable() {
public void run() {
while (true) {
// 锁定
threadLock.lock();
try {
if ( count < 1) {
return;
}
if (!flag) {
// aThread的任务
System.out.println("bThread --> " + (count--));
flag = !flag;
}
} catch (Exception e) {
// TODO: handle exception
} finally {
// 释放锁
threadLock.unlock();
}
}
}
}); public void startTwoThread() {
aThread.start();
bThread.start();
} public static void main(String[] args) {
TwoThreadPrinter twoThreadPrinter = new TwoThreadPrinter();
twoThreadPrinter.startTwoThread();
} }
用synchronized实现：
package com.yjq.thread_demo;
public class TwoThreadPrinter2 {
private Object threadLock = new Object();
int count =10;
Thread aThread = new Thread(new Runnable() {
public void run() {
while (true) {
// 锁定
synchronized (threadLock) {
if ( count < 1) {
return;
}
// // aThread的任务
System.out.println("aThread --> " + (count--));
threadLock.notify();
try {
threadLock.wait();
} catch (Exception e) {
// TODO: handle exception
}
}
}
}
});
Thread bThread = new Thread(new Runnable() {
public void run() {
while (true) {
// 锁定
synchronized (threadLock) {
if ( count < 1) {
return;
}
// // aThread的任务
System.out.println("bThread --> " + (count--));
threadLock.notify();
try {
threadLock.wait();
} catch (Exception e) {
// TODO: handle exception
}
}
}
}
});
public void startTwoThread() {
aThread.start();
bThread.start();
}
public static void main(String[] args) {
TwoThreadPrinter twoThreadPrinter = new TwoThreadPrinter();
twoThreadPrinter.startTwoThread();
}
}
用Lock类的方法比較easy理解。 lock() 和 unlock()之间的块是被锁定的
用synchronize的方法少用了个flag来标志轮到哪个线程来打印，这是由于线程锁的notifity( )方法会释放锁并唤醒其它线程 ，线程锁的wait( )方法则是释放锁并休眠当前线程,假设刚好仅仅有两个线程，那么自然就是開始还有一个线程而休眠本线程。
二.扩展到n个线程轮流打印数字的问题
n个线程轮流打印数字。用Lock类是比較easy扩展的
比方三个线程轮流打印数字
package com.myexample.test; import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock; public class ThreeThreadPrinter { private Lock threadLock = new ReentrantLock(); private int flag = 0; int count =10; Thread aThread = new Thread(new Runnable() {
public void run() {
while (true) {
// 锁定
threadLock.lock();
try {
if ( count < 1) {
return;
}
if (count%3 == 0 ) {
// aThread的任务
System.out.println("aThread --> " + count);
count--;
}
} catch (Exception e) {
// TODO: handle exception
} finally {
// 释放锁
threadLock.unlock();
}
}
}
}); Thread bThread = new Thread(new Runnable() {
public void run() {
while (true) {
// 锁定
threadLock.lock();
try {
if ( count < 1) {
return;
}
if (count%3 == 1 ) {
// aThread的任务
System.out.println("bThread --> " + count);
count--;
}
} catch (Exception e) {
// TODO: handle exception
} finally {
// 释放锁
threadLock.unlock();
}
}
}
}); Thread cThread = new Thread(new Runnable() {
public void run() {
while (true) {
// 锁定
threadLock.lock();
try {
if ( count < 1) {
return;
}
if (count%3 == 2 ) {
// aThread的任务
System.out.println("cThread --> " + count);
count--;
}
} catch (Exception e) {
// TODO: handle exception
} finally {
// 释放锁
threadLock.unlock();
}
}
}
}); public void startTwoThread() {
aThread.start();
bThread.start();
cThread.start();
} public static void main(String[] args) {
ThreeThreadPrinter twoThreadPrinter = new ThreeThreadPrinter();
twoThreadPrinter.startTwoThread();
} }
输出结果
bThread --> 10
aThread --> 9
cThread --> 8
bThread --> 7
aThread --> 6
cThread --> 5
bThread --> 4
aThread --> 3
cThread --> 2
bThread --> 1
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