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所谓的原子量即操作变量的操作是“原子的”，该操作不可再分，因此是线程安全的。为何要使用原子变量呢，原因是多个线程对单个变量操作也会引起一些问题。在Java5之前，可以通过volatile、synchronized关键字来解决并发访问的安全问题，但这样太麻烦。Java5之后，专门提供了用来进行单变量多线程并发安全访问的工具包java.util.concurrent.atomic，其中的类也很简单
package unit_fifteen; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.atomic.AtomicLong; /** * Java线程：新特征-原子量 * */ public class Test { public static void main(String[] args) { ExecutorService pool = Executors.newFixedThreadPool(2); Runnable t1 = new MyRunnable("张三", 2000); Runnable t2 = new MyRunnable("李四", 3600); Runnable t3 = new MyRunnable("王五", 2700); Runnable t4 = new MyRunnable("老张", 600); Runnable t5 = new MyRunnable("老牛", 1300); Runnable t6 = new MyRunnable("胖子", 800); //执行各个线程 pool.execute(t1); pool.execute(t2); pool.execute(t3); pool.execute(t4); pool.execute(t5); pool.execute(t6); //关闭线程池 pool.shutdown(); } } class MyRunnable implements Runnable { private static AtomicLong aLong =new AtomicLong(10000); //原子量，每个线程都可以自由操作 private String name; //操作人 private int x; //操作数额 MyRunnable(String name, int x) { this.name = name; this.x = x; } public void run() { System.out.println(name + "执行了" + x +"，当前余额：" + aLong.addAndGet(x)); } }
上面是个反例，代码的结果是多变的
注意：原子量虽然可以保证单个变量在某一个操作过程的安全，但无法保证你整个代码块，或者整个程序的安全性。因此，通常还应该使用锁等同步机制来控制整个程序的安全性
package unit_fifteen; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReentrantLock; import java.util.concurrent.atomic.AtomicLong; /** * Java线程：新特征-原子量 * */ public class Test { public static void main(String[] args) { ExecutorService pool = Executors.newFixedThreadPool(2); Lock lock = new ReentrantLock(false); Runnable t1 = new MyRunnable("张三", 2000,lock); Runnable t2 = new MyRunnable("李四", 3600,lock); Runnable t3 = new MyRunnable("王五", 2700,lock); Runnable t4 = new MyRunnable("老张", 600,lock); Runnable t5 = new MyRunnable("老牛", 1300,lock); Runnable t6 = new MyRunnable("胖子", 800,lock); //执行各个线程 pool.execute(t1); pool.execute(t2); pool.execute(t3); pool.execute(t4); pool.execute(t5); pool.execute(t6); //关闭线程池 pool.shutdown(); } } class MyRunnable implements Runnable { private static AtomicLong aLong =new AtomicLong(10000); //原子量，每个线程都可以自由操作 private String name; //操作人 private int x; //操作数额 private Lock lock; MyRunnable(String name, int x,Lock lock) { this.name = name; this.x = x; this.lock = lock; } public void run() { lock.lock(); System.out.println(name + "执行了" + x +"，当前余额：" + aLong.addAndGet(x)); lock.unlock(); } }
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原文地址：http://www.cnblogs.com/yyxiangjava/p/5833721.html
