如何正确的停止一個線程

/**
 * @author VicterTian
 * @version V1.0
 * @Date 2018/12/11
 */
public class ThreadTest09 {
  public static void main(String[] args) {
    //Runnable r1 = new Processor();
    Processor r1 = new Processor();
    Thread t1 = new Thread(r1, "t1");
    t1.start();
    try {
      Thread.sleep(2000);
    } catch (Exception e) {
      e.printStackTrace();
    }
    //停止線程
    System.out.println("開始停止線程");
    r1.setFlag();
  }
}

class Processor implements Runnable {
  //線程停止标記，true為停止
  private Boolean flag = true;
  public void run() {
    for (int i = 1; i < 100; i++) {
      try {
        Thread.sleep(1000);
      } catch (Exception e) {
        e.printStackTrace();
      }
      if (flag) {
        System.out.println(Thread.currentThread().getName() + "," + i);
      }else{
        break;
      }
    }
  }
  void setFlag() {
    this.flag = false;
  }
}