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:itjdk1.8injava -Didea.launcher.port=7532 "-Didea.launcher.bin.path=D:itideaIntelliJ IDEA 2016.3.3in" -Dfile.encoding=UTF-8 -classpath "D:itjdk1.8jrelibcharsets.jar;D:itjdk1.8jrelibdeploy.jar;D:itjdk1.8jrelibextaccess-bridge-64.jar;D:itjdk1.8jrelibextcldrdata.jar;D:itjdk1.8jrelibextdnsns.jar;D:itjdk1.8jrelibextjaccess.jar;D:itjdk1.8jrelibextjfxrt.jar;D:itjdk1.8jrelibextlocaledata.jar;D:itjdk1.8jrelibext ashorn.jar;D:itjdk1.8jrelibextsunec.jar;D:itjdk1.8jrelibextsunjce_provider.jar;D:itjdk1.8jrelibextsunmscapi.jar;D:itjdk1.8jrelibextsunpkcs11.jar;D:itjdk1.8jrelibextzipfs.jar;D:itjdk1.8jrelibjavaws.jar;D:itjdk1.8jrelibjce.jar;D:itjdk1.8jrelibjfr.jar;D:itjdk1.8jrelibjfxswt.jar;D:itjdk1.8jrelibjsse.jar;D:itjdk1.8jrelibmanagement-agent.jar;D:itjdk1.8jrelibplugin.jar;D:itjdk1.8jrelib esources.jar;D:itjdk1.8jrelib t.jar;F:springboot hreaddemooutproduction hreaddemo;D:itideaIntelliJ IDEA 2016.3.3libidea_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。