2.1.5脏读

虽然在赋值的时候进行了同步，但是在取值的时候会出问题，这就叫做脏读。

发生脏读说明在读取实例变量的值的时候，此值已经被其他线程改过了。

测试如下

package com.cky.bean;

/**
 * Created by chenkaiyang on 2017/12/5.
 */
public class MyObject {
    public String usrName= "A";
    public String pwd = "AA";
    synchronized public void setValue(String usrName, String pwd) {
        try {
            this.usrName = usrName;
            Thread.sleep(5000);
            this.pwd = pwd;
            System.out.println("setValue method name=" + Thread.currentThread().getName() +" usrName="+ usrName+ " pwd="+ pwd);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }

     public void getValue() {
        System.out.println("getValue method name=" + Thread.currentThread().getName() +" usrName="+ usrName+ " pwd="+ pwd);
    }
}

package com.cky.thread;

import com.cky.bean.MyObject;

/**
 * Created by chenkaiyang on 2017/12/5.
 */
public class ThreadA extends Thread{
    private MyObject mo;
    public ThreadA(MyObject mo) {
        super();
        this.mo = mo;
    }

    @Override
    public void run() {
        super.run();
        mo.setValue("B", "BB");
    }
}

package com.cky.test;

import com.cky.bean.MyObject;
import com.cky.thread.ThreadA;

/**
 * Created by chenkaiyang on 2017/12/2.
 */
public class Test {
    public static void main(String[] args){
        try {
            MyObject myObject = new MyObject();
            ThreadA threadA = new ThreadA(myObject);
            threadA.start();
            Thread.sleep(2000);//打印结果受到这个睡眠时间大小的影响
            myObject.getValue();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }
}

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
getValue method name=main usrName=B pwd=AA
setValue method name=Thread-0 usrName=B pwd=BB

Process finished with exit code 0

出现结果分析：

出现脏读是因为getValue方法不是同步的，所以可以在任意时候进行调用。

解决方案：加上synchronized

synchronized public void getValue() {
        System.out.println("getValue method name=" + Thread.currentThread().getName() +" usrName="+ usrName+ " pwd="+ pwd);
    }

D:\it\jdk1.8\bin\java -Didea.launcher.port=7535 "-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
setValue method name=Thread-0 usrName=B pwd=BB
getValue method name=main usrName=B pwd=BB