标签：trace als print rac eth closed import create 技术分享
一、接上一步，如果变量在方法外部，对变量加上关键字synchonzied即可
变量加synchronized
package service; /** * Created by zhc on 2017/10/10 */ public class HasSelfPrivateNum { private int num = 0; synchronized public void addI(String username) { try { if (username.equals("a")) { num = 100; System.out.println("a is set over"); } else { num = 200; System.out.println("b is set over"); } System.out.println(username + " num = " + num); } catch (Exception e) { e.printStackTrace(); } } }
二、出现脏读情况
首先给出一个实体类，通俗讲，set方法进行加锁，get没有
package entity; /** * Created by zhc on 2017/10/10 */ public class PublicVar { public String username = "A"; public String password = "AA"; synchronized public void setValue(String username,String password){ try { this.username = username; Thread.sleep(5000); this.password = password; System.out.println(" setValue method thread name "+Thread.currentThread().getName() +"username and password ="+username+" "+password); }catch (InterruptedException e){ e.printStackTrace(); } } public void getValue(){ System.out.println(" getValue method thread name "+Thread.currentThread().getName() +"username and password ="+username+" "+password); } }
然后线程进行设值，然后读取。
package extthread; import entity.PublicVar; /** * Created by zhc on 2017/10/10 */ public class ThreadC extends Thread { private PublicVar publicVar; public ThreadC(PublicVar publicVar){ super(); this.publicVar = publicVar; } @Override public void run() { super.run(); publicVar.setValue("B","BB"); } }
开启线程，进行测验
Run出现结果：
getValue method thread name main username and password =B AA
setValue method thread name Thread-0 username and password =B BB
出现脏读情况，发现synchronized某方法（set），可以获得此方法锁，也就是获得该对象锁，但是get方法因为未被synchronized，则被调用时无关是否被锁。
但是如果get方法也被synchronized，那么B线程的get方法调用一定要等A线程执行完set先结束才行。
我们对get方法加synchronized，
package entity; /** * Created by zhc on 2017/10/10 */ public class PublicVar { public String username = "A"; public String password = "AA"; synchronized public void setValue(String username,String password){ try { this.username = username; Thread.sleep(5000); this.password = password; System.out.println(" setValue method thread name "+Thread.currentThread().getName() +" username and password ="+username+" "+password); }catch (InterruptedException e){ e.printStackTrace(); } } synchronized public void getValue(){ System.out.println(" getValue method thread name "+Thread.currentThread().getName() +" username and password ="+username+" "+password); } }
看看结果：
setValue method thread name Thread-0 username and password =B BB
getValue method thread name main username and password =B BB
对象及变量的并发访问-----synchronized同步（2）----- 脏读
标签：trace als print rac eth closed import create 技术分享
原文地址：http://www.cnblogs.com/zhc-nice/p/7644610.html
