java面试题二十九 多线程数据共享问题

public class TestThread {

public static void main(String[] args) {
NewThread nt=new NewThread();
new Thread(nt).start();
new Thread(nt).start();
new Thread(nt).start();
new Thread(nt).start();

}

}
class NewThread  implements Runnable
{
int j=0;
String runThreadName = null;
public  void run()
{

while(true)
{
synchronized(this){
try {
Thread.sleep(1000);
runThreadName = Operation(Thread.currentThread().getName());
System.out.println(runThreadName+" : j = " +j);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}

}
public String Operation(String threadName){
int operation  = Integer.parseInt(threadName.split("-")[1]);
String name = null;
switch(operation){
case 0: j++;name="自增线程1";break;
case 1: j++;name="自增线程2";break;
case 2: j--;name="自减线程3";break;
case 3: j--;name="自减线程4";break;
}

return name;
}
}