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java synchronized(一)

2024-08-07 09:34:28   215人阅读

java synchronized主要用于控制线程同步，中间有很多小的细节，知识，这里我简单的整理一下，做个记录。主要用于方法和代码块的控制

先说说方法控制

模拟银行存款和取款，创建一个Account类，两个属性，一个name和accout。先存1w进去，在用一100个线程取钱1k和存1k。等待所有线程结束后，输出account。没有synchronized控制会造成account不等于1w。使用了synchronized结果正确，性能降低了很多。下面贴一下代码

参考：http://www.cnblogs.com/devinzhang/archive/2011/12/14/2287675.html

Account.java

 1 package com.gxf.thread; 2  3 public class Account { 4     public String name; 5     public float amount; 6      7     public Account(String name, float amount){ 8         this.name = name; 9         this.amount = amount;10     }11     12     /**13      * 模拟存钱14      * @param amt15      */16     public synchronized void deposit(float amt){17         float tmp = amount;18         tmp += amt;19         try {20             Thread.sleep(100);21         } catch (InterruptedException e) {22             23             e.printStackTrace();24         }25         this.amount = tmp;26     }27     28     /**29      * 模拟取钱30      * @param amt31      */32     public synchronized void withdraw(float amt){33         float tmp = amount;34         tmp -= amt;35         try {36             Thread.sleep(100);37         } catch (InterruptedException e) {38 39             e.printStackTrace();40         }41         42         amount = tmp;43     }44 }

测试类AccountTest.java

 1 package com.gxf.thread; 2  3 public class AccountTest { 4  5     public static void main(String[] args) { 6         final int NUM_THREADS = 5;                    //线程总数 7         Thread threads[] = new Thread[NUM_THREADS]; 8         final Account zhangsan = new Account("zhangsan", 10000);        //张三存1w到银行 9         10         //1000个线程对张三账户进行存钱1k和取1k11         for(int i = 0; i < NUM_THREADS; i++){12             threads[i] = new Thread(new Runnable(){13 14                 @Override15                 public void run() {16                     zhangsan.deposit(1000);17                     zhangsan.withdraw(1000);18                 }19                 20             });21             threads[i].start();                        //线程开始22         }23         //等待所有线程结束24         for(int i = 0; i < NUM_THREADS; i++){25             try {26                 threads[i].join();                    //等待该线程结束27             } catch (InterruptedException e) {28                 // TODO Auto-generated catch block29                 e.printStackTrace();30             }31         }32         System.out.println("account = " + zhangsan.amount);33     }34 35 }

还有就是修饰一个代码块

参考：http://javacrazyer.iteye.com/blog/759300/

类LockThread向屏幕输出1-9

两个线程同时访问lockThread向屏幕输出的方法，不同步将会输出如：1 1 2 2 3 3...用了同步输出如:1 2 3 ...1 2 3...

LockThread.java

 1 package com.gxf.thread; 2  3 public class LockThread implements Runnable { 4  5     @Override 6     public void run() { 7         synchronized(this){ 8             for(int i = 1; i < 10; i++){ 9                 System.out.println(i);10                 try {11                     Thread.sleep(1000);12                 } catch (InterruptedException e) {13                     14                     e.printStackTrace();15                 }16             }17         }18 19     }20 21 }

测试代码

LockThreadTest.java

 1 package com.gxf.thread; 2  3 public class LockThreadTest { 4  5     public static void main(String[] args) { 6         LockThread lockThread = new LockThread(); 7         Thread thread1 = new Thread(lockThread); 8         Thread thread2 = new Thread(lockThread); 9         10         thread1.start();11         thread2.start();12 13     }14 15 }

ps:我也没检查synchronized拼对没有~

java synchronized(一)


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