synchronized是一个重量级锁,我们都知道该关键字锁住的是对象而不是代码本身,那么对于静态方法和同步方法有什么不同呢,通过如下代码进行测试
1 public class SynchronizedTest { 2 3 private static int num; 4 5 private synchronized void test(String param){ 6 if(StringUtils.equals(param,"a")){ 7 num = 100; 8 System.out.println("set " + param + " num over"); 9 try { 10 Thread.sleep(1000); 11 } catch (InterruptedException e) { 12 e.printStackTrace(); 13 } 14 }else{ 15 num = 200; 16 System.out.println("set " + param + " num over"); 17 } 18 System.out.println("i am : " + param + "; num = " + num); 19 } 20 21 public static void main(String[] args){ 22 SynchronizedTest s1 = new SynchronizedTest(); 23 SynchronizedTest s2 = new SynchronizedTest(); 24 25 new Thread(new Runnable() { 26 @Override 27 public void run() { 28 s1.test("a"); 29 } 30 }).start(); 31 32 new Thread(new Runnable() { 33 @Override 34 public void run() { 35 s2.test("b"); 36 } 37 }).start(); 38 } 39 }
set a num over set b num over i am : b; num = 200 i am : a; num = 200 Process finished with exit code 0
我们可以看出两个不同的对象s1和s2并没有互斥,因为这里synchronized是分别持有两个对象的锁。如果要想m1,m2两个对象竞争同一个锁，则需要在method01()上加上static修饰,如下:
1 public class SynchronizedTest { 2 3 private static int num; 4 5 private synchronized static void test(String param){ 6 if(StringUtils.equals(param,"a")){ 7 num = 100; 8 System.out.println("set " + param + " num over"); 9 try { 10 Thread.sleep(1000); 11 } catch (InterruptedException e) { 12 e.printStackTrace(); 13 } 14 }else{ 15 num = 200; 16 System.out.println("set " + param + " num over"); 17 } 18 System.out.println("i am : " + param + "; num = " + num); 19 } 20 21 public static void main(String[] args){ 22 SynchronizedTest s1 = new SynchronizedTest(); 23 SynchronizedTest s2 = new SynchronizedTest(); 24 25 new Thread(new Runnable() { 26 @Override 27 public void run() { 28 s1.test("a"); 29 } 30 }).start(); 31 32 new Thread(new Runnable() { 33 @Override 34 public void run() { 35 s2.test("b"); 36 } 37 }).start(); 38 } 39 }
运行结果：
set a num over i am : a; num = 100 set b num over i am : b; num = 200 Process finished with exit code 0
synchronized修饰不加static的方法，锁是加在单个对象上，不同的对象没有竞争关系；修饰加了static的方法，锁是加载类上，这个类所有的对象竞争一把锁.
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原文链接：https://blog.csdn.net/LQM1991/article/details/86143278
原文：https://www.cnblogs.com/hongdalin/p/11492192.html
