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對同一個對象進行多線程操作時，如何保證線程執行結果的一致性？我們需要對線程操作對象加同步鎖。（這是一道面試題）
需求描述
1-20個數字
A線程打印奇數：1，3，5，7，9，11，13，15，17，19
B線程打印偶數：2，4，6，8，10，12，14，16，18，20
C線程在AB兩個線程執行完了之后打印結果：“success”。
線程代碼實現
Num.java
package com.boonya.thread.test;
/**
* @ClassName: Num
* @Description: TODO(加鎖計算對象)
* @author: pengjunlin
* @motto: 學習需要毅力，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(奇數線程)
* @author: pengjunlin
* @motto: 學習需要毅力，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(偶數線程)
* @author: pengjunlin
* @motto: 學習需要毅力，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(等待結果線程)
* @author: pengjunlin
* @motto: 學習需要毅力，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(線程測試)
* @author: pengjunlin
* @motto: 學習需要毅力，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();
}
}
測試結果
"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 作為方法塊使用時需要只能對對象加鎖，不能是常用數據類型。
AB線程改進:使用線程等待和通知
AThread.java
package com.boonya.thread.test;
/**
* @ClassName: AThread
* @Description: TODO(奇數線程)
* @author: pengjunlin
* @motto: 學習需要毅力，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(偶數線程)
* @author: pengjunlin
* @motto: 學習需要毅力，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：線程等待和通知的操作是節省CPU運算的一種方式，避免CPU空轉（線程方法一直不停地跑類似于死循環是很可怕的），如果是要讓線程停下來需要調用線程的wait()。
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