如何正确的停止一个线程

package gov.mof.fasp2.gcfr.adjustoffset.adjust;

public class Main {
    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(20);
        }catch(Exception e) {}
        
        //停止线程
        r1.setFlag(true);
　　　　　System.out.println("mainEnd");
    }    
}
class Processor implements Runnable {
    
    //线程停止标记，true为停止
    private boolean flag;
    
    public void run() {
        for (int i=1; i<100; i++) {
            System.out.println(Thread.currentThread().getName() + "," + i);
            //为true停止线程执行
            if (flag) {
                break;
            }
        }    
    }
    public void setFlag(boolean flag) {
        this.flag = flag;
    }    
}