在Java如何保证方法是线程安全的
废话开篇
都说Java程序好些,但是我觉得Java编程这东西,没个十年八年的真不敢说自己精通Java编程,由于工作原因,开始转战Java多线程,以前没怎么接触过,所以想留点脚印在这两条路上。
切入正题
开门见山,今天看到别人写的一段关于方法是否线程安全的文章,比较简单,但是由于自己也是刚开始入门,所以就迈下了第一步。由于注释还算比较详细,所以就不废话了,直接上code。
此方法不是线程安全的
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1 /** 2 * @Title: NotThreadSafeCounter.java 3 * @Package never.uncategory 4 * @Description: * The method is not thread-safe, because the 5 * counter++ operation is not atomic, which means it consists 6 * more than one atomic operations. In this case, one is 7 * accessing value and the other is increasing the value by one. 8 * @author "Never" xzllc2010#gmail.com 9 * @date Mar 14, 2014 7:44:24 PM 10 */ 11 /* 12 13 */ 14 package never.uncategory; 15 16 public class NotThreadSafeCounter extends Thread { 17 18 private static int counter = 0; 19 20 public void run() { 21 System.out.println("counter:" + getCount()); 22 } 23 24 public static int getCount() { 25 26 try { 27 Thread.sleep(1500); 28 } catch (Exception e) { 29 e.printStackTrace(); 30 } 31 return counter++; 32 33 } 34 35 public static void main(String[] args) { 36 37 for (int i = 0; i < 5; i++) { 38 new NotThreadSafeCounter().start(); 39 } 40 } 41 42 }
此方法是线程安全的(synchronized)
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1 /** 2 * @Title: ThreadSafeCounter.java 3 * @Package never.uncategory 4 * @Description: Adding synchronized to this method will makes 5 * it thread-safe,When synchronized is added to a static method, 6 * the Class object is the object which is locked.If the method 7 * is not static, then adding synchronized keyword willsynchronize 8 * the instance of the class, not the Class object. 9 * @author "Never" xzllc2010#gmail.com 10 * @date Mar 14, 2014 8:09:45 PM 11 */ 12 package never.uncategory; 13 14 public class ThreadSafeCounter { 15 16 private static int counter = 0; 17 18 public void run() { 19 System.out.println("counter:" + getCount()); 20 } 21 22 public static synchronized int getCount() { 23 return counter++; 24 } 25 26 public static void main(String[] args) { 27 28 for (int i = 0; i < 5; i++) { 29 new NotThreadSafeCounter().start(); 30 } 31 } 32 33 }
此方法也是线程安全的(AtomicInteger)
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1 /** 2 * @Title: ThreadSafeCounter2.java 3 * @Package never.uncategory 4 * @Description: using AtomicInteger for safe counter 5 * @author "Never" xzllc2010#gmail.com 6 * @date Mar 14, 2014 8:14:33 PM 7 */ 8 package never.uncategory; 9 10 import java.util.concurrent.atomic.AtomicInteger; 11 12 public class ThreadSafeCounter2 { 13 14 private static AtomicInteger counter = new AtomicInteger(0); 15 16 public void run() { 17 System.out.println("counter:" + getCount()); 18 } 19 20 public static int getCount() { 21 return counter.getAndIncrement(); 22 } 23 24 public static void main(String[] args) { 25 26 for (int i = 0; i < 5; i++) { 27 new NotThreadSafeCounter().start(); 28 } 29 } 30 }
时光的尾巴
刚入门,如有疑问,多指教和交流。