java多线程的一个简单问题

Question

该线程是一个求某个数的素数总个数

利用多线程来操作
为什么创建一个实现Runnable接口的对象
其他线程共享该对象 输出结果却是各自工作的结果 素数总和也不对
package Reflect;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class Threaddemo {
public static void main(String[] args) {
test t =new test(10);
new Thread(t,"Thread1").start();
new Thread(t,"Thread2").start();
new Thread(t,"Thread3").start();
new Thread(t,"Thread4").start();
new Thread(t,"Thread5").start();
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println(t.getNum()+"以内的素数和:"+PrimeMethod.account);
}
}
class test implements Runnable{
final Lock lock =new ReentrantLock();
private int num;
test(int num){
this.num=num;
}
public int getNum(){
return num;
}
public void run() {
for(int i=num;i>1;i--){
if(PrimeMethod.isPrime(i)){
lock.lock();
System.out.println(Thread.currentThread().getName()+"输出一个质数:"+i);
PrimeMethod.account++;
lock.unlock();
}
}
}
}
class PrimeMethod{
static int account =0;
public static boolean isPrime(long i){
for(long j=2;j<=Math.sqrt(i);j++)
if(i%j==0)
return false;
return true;
}
}
输出结果如图
求大神解答 谢谢

Answer 1

用volatile修饰一下

 volatile static int account =0;