Java使用原子类进行多线程的 i++ 操作示例

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使用AtomicInteger原子类进行 i ++ 操作可以有类似 synchronized 实现同步的效果。

原子操作是不能分割的整体，没有其他线程能够中断或检查正在原子操作中的变量。一个原子类型就是一个原子操作可用的类型，它可以在没有锁的情况下做到线程安全。

示例1：

AddCountThread.java

import java.util.concurrent.atomic.AtomicInteger;public class AddCountThread extends Thread {private AtomicInteger count = new AtomicInteger(0);@Overridepublic void run() {for(int i=0;i<10000;i++){System.out.println(count.incrementAndGet());}}
}

Run_Atomic.java

public class Run_Atomic {public static void main(String[] args) {AddCountThread countService = new AddCountThread();Thread t1 = new Thread(countService);t1.start();Thread t2 = new Thread(countService);t2.start();Thread t3 = new Thread(countService);t3.start();Thread t4 = new Thread(countService);t4.start();Thread t5 = new Thread(countService);t5.start();}
}

输出结果成功地累加到 50000

但是原子类也并不是完全安全的，比如以下例子

示例2：

MyService.java

import java.util.concurrent.atomic.AtomicLong;public class MyService {public static AtomicLong aiRef = new AtomicLong();public void addNum() {System.out.println(Thread.currentThread().getName() + "加了100之后的结果是：" + aiRef.addAndGet(100));aiRef.addAndGet(1);}
}

MyThread.java

public class MyThread extends Thread {private MyService myService;public MyThread (MyService myService) {super();this.myService = myService;}@Overridepublic void run() {myService.addNum();}
}

Run3_1.java

public class Run3_1 {public static void main(String[] args) {try {MyService myService = new MyService();MyThread[] array = new MyThread[8];for(int i=0;i<array.length;i++) {array[i] = new MyThread(myService);}for (int i = 0;i<array.length;i++ ){array[i].start();}Thread.sleep(1000);System.out.println(myService.aiRef.get());}catch (InterruptedException e) {e.printStackTrace();}}
}

输出结果：