有问题的

package com.bjpowernode.t13;

import java.time.Duration;
import java.time.LocalTime;

public class Processor implements Runnable {

private int num;


/*
下面在方法上加入synchronized关键字，会有性能问题
*/
@Override
public synchronized void run() {
LocalTime begin = LocalTime.now();
//------下面的代码不会出现线程安全问题------
System.out.println("模拟其他非线程安全的操作");

try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}

//------上面的代码不会出现线程安全问题------

for (int i = 0; i < 5; i++) {
num += i;
}

System.out.println(Thread.currentThread().getName() + "------->" + num);

//将num重新设置为0，保证其他线程在运行的时候num是0
num = 0;

//------下面的代码不会出现线程安全问题------
System.out.println("模拟其他非线程安全的操作");
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
//------上面的代码不会出现线程安全问题------

LocalTime end = LocalTime.now();

Duration between = Duration.between(begin, end);
System.out.println(Thread.currentThread().getName() +"运行耗时： " + between.getSeconds() +"秒");
}

}

------------------

package com.bjpowernode.t13;

public class Test {

public static void main(String[] args) {
//只创建一个Processor
Processor p = new Processor();

Thread t1 = new Thread(p,"t1");
Thread t2 = new Thread(p,"t2");

t1.start();
t2.start();
}

}