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) {
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();
}
}
}
}
}
}
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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