Java线程使用同步锁交替执行打印奇数偶数的方法

Java线程使用同步锁交替执行打印奇数偶数的方法

对同一个对象进行多线程操作时，如何保证线程执行结果的一致性？我们需要对线程操作对象加同步锁。（这是一道面试题）

需求描述

1-20个数字

A线程打印奇数：1，3，5，7，9，11，13，15，17，19

B线程打印偶数：2，4，6，8，10，12，14，16，18，20

C线程在AB两个线程执行完了之后打印结果：“success”。

线程代码实现

Num.java

package com.boonya.thread.test;

/**

* @ClassName: Num

* @Description: TODO(加锁计算对象)

* @author: pengjunlin

* @motto: 学习需要毅力，那就秀毅力

* @date 2019-01-14 22:47

*/

public class Num {

int value=1;

}

AThread.java

package com.boonya.thread.test;

/**

* @ClassName: AThread

* @Description: TODO(奇数线程)

* @author: pengjunlin

* @motto: 学习需要毅力，那就秀毅力

* @date 2019-01-14 22:26

*/

public class AThread implements Runnable{

Num num;

public AThread(Num num){

this.num=num;

}

public void run() {

while (num.value<20){

synchronized (num){

if(num.value%2!=0){

System.out.println("AThread:"+ num.value);

num.value++;

}

}

}

}

}

BThread.java

package com.boonya.thread.test;

/**

* @ClassName: BThread

* @Description: TODO(偶数线程)

* @author: pengjunlin

* @motto: 学习需要毅力，那就秀毅力

* @date 2019-01-14 22:26

*/

public class BThread implements Runnable {

Num num;

public BThread(Num num){

this.num=num;

}

public void run() {

while (num.value<=20){

synchronized (num){

if(num.value%2==0){

System.out.println("BThread:"+ num.value);

num.value++;

}

}

}

}

}

CThread.java

package com.boonya.thread.test;

/**

* @ClassName: CThread

* @Description: TODO(等待结果线程)

* @author: pengjunlin

* @motto: 学习需要毅力，那就秀毅力

* @date 2019-01-14 22:26

*/

public class CThread implements Runnable {

Num num;

public CThread(Num num){

this.num=num;

}

public void run() {

while (num.value<20){

try {

Thread.sleep(1);

} catch (InterruptedException e) {

e.printStackTrace();

}

}

System.out.println("CThread:success!");

}

}

MainTest.java

package com.boonya.thread.test;

import java.util.ArrayList;

import java.util.List;

/**

* @ClassName: MainTest

* @Description: TODO(线程测试)

* @author: pengjunlin

* @motto: 学习需要毅力，那就秀毅力

* @date 2019-01-14 21:54

*/

public class MainTest {

public static void main(String[] args) {

Num num=new Num();

Thread a=new Thread(new AThread(num));

Thread b=new Thread(new BThread(num));

Thread c=new Thread(new CThread(num));

a.start();

b.start();

c.start();

}

}

测试结果

"C:\Program Files\Java\jdk1.8.0_121\bin\java" "-javaagent:C:\Users\boonya\AppData\Roaming\JetBrains\IntelliJ IDEA 2017.2.5\lib\idea_rt.jar=51911:C:\Users\boonya\AppData\Roaming\JetBrains\IntelliJ IDEA 2017.2.5\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_121\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\rt.jar;C:\Users\boonya\Desktop\JavaAlgorithm\target\test-classes;C:\Users\boonya\Desktop\JavaAlgorithm\target\classes" com.boonya.thread.test.MainTest

AThread:1

BThread:2

AThread:3

BThread:4

AThread:5

BThread:6

AThread:7

BThread:8

AThread:9

BThread:10

AThread:11

BThread:12

AThread:13

BThread:14

AThread:15

BThread:16

AThread:17

BThread:18

AThread:19

BThread:20

CThread:success!

Process finished with exit code 0

注意：synchronized 作为方法块使用时需要只能对对象加锁，不能是常用数据类型。

AB线程改进:使用线程等待和通知

AThread.java

package com.boonya.thread.test;

/**

* @ClassName: AThread

* @Description: TODO(奇数线程)

* @author: pengjunlin

* @motto: 学习需要毅力，那就秀毅力

* @date 2019-01-14 22:26

*/

public class AThread implements Runnable{

Num num;

public AThread(Num num){

this.num=num;

}

public void run() {

while (num.value<20){

synchronized (num){

if(num.value%2!=0){

System.out.println("AThread:"+ num.value);

num.value++;

//num.notify();

num.notifyAll();

}else{

try {

num.wait();

} catch (InterruptedException e) {

BsQfsBrIn e.printStackTrace();

}

}

}

}

}

}

BThread.java

package com.boonya.thread.test;

/**

* @ClassName: BThread

* @Description: TODO(偶数线程)

* @author: pengjunlin

* @motto: 学习需要毅力，那就秀毅力

* @date 2019-01-14 22:26

*/

public class BThread implements Runnable {

Num num;

public BThread(Num num){

this.num=num;

}

public void run() {

while (num.value<=20){

synchronized (num){

if(num.value%2==0){

System.out.println("BThread:"+ num.value);

num.value++;

//num.notify();

num.notifyAll();

}else{

try {

num.wait();

} catch (InterruptedException e) {

e.printStackTrace();

}

http:// }

}

}

}

}

注：线程等待和通知的操作是节省CPU运算的一种方式，避免CPU空转（线程方法一直不停地跑类似于死循环是很可怕的），如果是要让线程停下来需要调用线程的wait()。

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