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
packagecom.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
*@date2019-01-1422:47
*/
publicclassNum{
intvalue=1;
}
AThread.java
packagecom.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
*@date2019-01-1422:26
*/
publicclassAThreadimplementsRunnable{
Numnum;
publicAThread(Numnum){
this.num=num;
}
publicvoidrun(){
while(num.value<20){
synchronized(num){
if(num.value%2!=0){
System.out.println("AThread:"+num.value);
num.value++;
}
}
}
}
}
BThread.java
packagecom.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
*@date2019-01-1422:26
*/
publicclassBThreadimplementsRunnable{
Numnum;
publicBThread(Numnum){
this.num=num;
}
publicvoidrun(){
while(num.value<=20){
synchronized(num){
if(num.value%2==0){
System.out.println("BThread:"+num.value);
num.value++;
}
}
}
}
}
CThread.java
packagecom.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
*@date2019-01-1422:26
*/
publicclassCThreadimplementsRunnable{
Numnum;
publicCThread(Numnum){
this.num=num;
}
publicvoidrun(){
while(num.value<20){
try{
Thread.sleep(1);
}catch(InterruptedExceptione){
e.printStackTrace();
}
}
System.out.println("CThread:success!");
}
}
MainTest.java
packagecom.boonya.thread.test;
importjava.util.ArrayList;
importjava.util.List;
/**
*@ClassName:MainTest
*@Description:TODO(线程测试)
*@author:pengjunlin
*@motto:学习需要毅力，那就秀毅力
*@date2019-01-1421:54
*/
publicclassMainTest{
publicstaticvoidmain(String[]args){
Numnum=newNum();
Threada=newThread(newAThread(num));
Threadb=newThread(newBThread(num));
Threadc=newThread(newCThread(num));
a.start();
b.start();
c.start();
}
}
测试结果
"C:\ProgramFiles\Java\jdk1.8.0_121\bin\java""-javaagent:C:\Users\boonya\AppData\Roaming\JetBrains\IntelliJIDEA2017.2.5\lib\idea_rt.jar=51911:C:\Users\boonya\AppData\Roaming\JetBrains\IntelliJIDEA2017.2.5\bin"-Dfile.encoding=UTF-8-classpath"C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\charsets.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\deploy.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\access-bridge-64.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\cldrdata.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\dnsns.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\jaccess.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\jfxrt.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\localedata.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\nashorn.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\sunec.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\sunjce_provider.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\sunmscapi.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\sunpkcs11.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\ext\zipfs.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\javaws.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\jce.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\jfr.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\jfxswt.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\jsse.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\management-agent.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\plugin.jar;C:\ProgramFiles\Java\jdk1.8.0_121\jre\lib\resources.jar;C:\ProgramFiles\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! Processfinishedwithexitcode0
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
packagecom.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
*@date2019-01-1422:26
*/
publicclassAThreadimplementsRunnable{
Numnum;
publicAThread(Numnum){
this.num=num;
}
publicvoidrun(){
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(InterruptedExceptione){
e.printStackTrace();
}
}
}
}
}
}
BThread.java
packagecom.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
*@date2019-01-1422:26
*/
publicclassBThreadimplementsRunnable{
Numnum;
publicBThread(Numnum){
this.num=num;
}
publicvoidrun(){
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(InterruptedExceptione){
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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