java中synchronized锁对象的问题总结

本人在业务执行中发现map中的数据打印有误,因此测试了一下,发现在使用synchronized时map对象是否使用static还是有很大的区别

代码简单,两个类,实例如下:

Main方法类

public class TestMain {    public static void main(String[] args) {        TestSyn t1 = new TestSyn();        TestSyn t2 = new TestSyn();        Thread ta = new Thread(t1, "A");        Thread tb = new Thread(t2, "B");        ta.start();        tb.start();    }}

Syn类
使用static修饰

public class TestSyn implements Runnable {    public static Map<String,String> smap = new HashMap<String,String>();    public void run() {        synchronized (smap) {            for (int i = 0; i < 5; i++) {                System.out.println(Thread.currentThread().getName() + " synchronized loop " + smap.size());                smap.put(i+"",Thread.currentThread().getName()+i);            }        }    }}

打印如下

A synchronized loop 0

A synchronized loop 1

A synchronized loop 2

A synchronized loop 3

A synchronized loop 4

B synchronized loop 5

B synchronized loop 5

B synchronized loop 5

B synchronized loop 5

B synchronized loop 5

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不使用static修饰

public class TestSyn implements Runnable {    public Map<String,String> smap = new HashMap<String,String>();    public void run() {        synchronized (smap) {            for (int i = 0; i < 5; i++) {                System.out.println(Thread.currentThread().getName() + " synchronized loop " + smap.size());                smap.put(i+"",Thread.currentThread().getName()+i);            }        }    }}

打印如下

A synchronized loop 0

A synchronized loop 1

A synchronized loop 2

A synchronized loop 3

A synchronized loop 4

B synchronized loop 0

B synchronized loop 1

B synchronized loop 2

B synchronized loop 3

B synchronized loop 4

代码执行结果,显示了在锁对象时,使用static和不使用的不同之处,如果要在同步代码块中使用map的内容的话就会造成问题,因此记录下来共勉