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
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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;
}
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athread.java
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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++;
}
}
}
}
}
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bthread.java
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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++;
}
}
}
}
}
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cthread.java
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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!");
}
}
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maintest.java
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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();
}
}
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测试结果
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"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
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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
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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();
}
}
}
}
}
}
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bthread.java
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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();
}
}
}
}
}
}
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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()。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：https://blog.csdn.net/boonya/article/details/86485504