2.1.1方法内的变量为线程安全

Posted 2020-10-16 成功的路上总是离不开贵人的帮助，名师的指点和小人的刺激。

非线程安全的问题存在于实例变量中，如果是方法内部的私有变量，则不存在非线程安全的问题，所以也就是线程安全了。

测试

 1 package com.cky.bean;
 2 
 3 /**
 4  * Created by chenkaiyang on 2017/12/4.
 5  */
 6 public class SelfPrivateNum {
 7 
 8     public void addI(String usrName) {
 9         try {
10             int num =0;
11             if (usrName.equals("a")) {
12                 num  =100;
13                 System.out.println("a over");
14                 Thread.sleep(2000);
15             } else {
16                 num= 200;
17                 System.out.println("b over");
18 
19             }
20             System.out.println(usrName + " num="+ num);
21         } catch (InterruptedException e) {
22             e.printStackTrace();
23         }
24     }
25 }

 1 package com.cky.thread;
 2 
 3 import com.cky.bean.SelfPrivateNum;
 4 
 5 /**
 6  * Created by chenkaiyang on 2017/12/4.
 7  */
 8 public class ThreadA  extends Thread{
 9     private SelfPrivateNum sn;
10     public ThreadA (SelfPrivateNum sn) {
11         this.sn = sn;
12     }
13     @Override
14     public void run() {
15         super.run();
16         sn.addI("a");
17     }
18 }

 1 package com.cky.thread;
 2 
 3 import com.cky.bean.SelfPrivateNum;
 4 
 5 /**
 6  * Created by chenkaiyang on 2017/12/4.
 7  */
 8 public class ThreadB extends Thread{
 9     private SelfPrivateNum sn;
10     public ThreadB (SelfPrivateNum sn) {
11         this.sn = sn;
12     }
13     @Override
14     public void run() {
15         super.run();
16         sn.addI("b");
17     }
18 }

 1 package com.cky.test;
 2 
 3 import com.cky.bean.SelfPrivateNum;
 4 import com.cky.thread.ThreadA;
 5 import com.cky.thread.ThreadB;
 6 
 7 /**
 8  * Created by chenkaiyang on 2017/12/2.
 9  */
10 public class Test {
11     public static void main(String[] args){
12         SelfPrivateNum sn = new SelfPrivateNum();
13         ThreadA threadA = new ThreadA(sn);
14         ThreadB threadB = new ThreadB(sn);
15         threadA.start();
16         threadB.start();
17     }
18 }

D:\it\jdk1.8\bin\java -Didea.launcher.port=7532 "-Didea.launcher.bin.path=D:\it\idea\IntelliJ IDEA 2016.3.3\bin" -Dfile.encoding=UTF-8 -classpath "D:\it\jdk1.8\jre\lib\charsets.jar;D:\it\jdk1.8\jre\lib\deploy.jar;D:\it\jdk1.8\jre\lib\ext\access-bridge-64.jar;D:\it\jdk1.8\jre\lib\ext\cldrdata.jar;D:\it\jdk1.8\jre\lib\ext\dnsns.jar;D:\it\jdk1.8\jre\lib\ext\jaccess.jar;D:\it\jdk1.8\jre\lib\ext\jfxrt.jar;D:\it\jdk1.8\jre\lib\ext\localedata.jar;D:\it\jdk1.8\jre\lib\ext\nashorn.jar;D:\it\jdk1.8\jre\lib\ext\sunec.jar;D:\it\jdk1.8\jre\lib\ext\sunjce_provider.jar;D:\it\jdk1.8\jre\lib\ext\sunmscapi.jar;D:\it\jdk1.8\jre\lib\ext\sunpkcs11.jar;D:\it\jdk1.8\jre\lib\ext\zipfs.jar;D:\it\jdk1.8\jre\lib\javaws.jar;D:\it\jdk1.8\jre\lib\jce.jar;D:\it\jdk1.8\jre\lib\jfr.jar;D:\it\jdk1.8\jre\lib\jfxswt.jar;D:\it\jdk1.8\jre\lib\jsse.jar;D:\it\jdk1.8\jre\lib\management-agent.jar;D:\it\jdk1.8\jre\lib\plugin.jar;D:\it\jdk1.8\jre\lib\resources.jar;D:\it\jdk1.8\jre\lib\rt.jar;F:\springboot\threaddemo\out\production\threaddemo;D:\it\idea\IntelliJ IDEA 2016.3.3\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain com.cky.test.Test
a over
b over
b num=200
a num=100

结果分析：

方法变量中不存在非线程安全的问题，永远都是线程安全的，这是方法内部变量是私有造成的。