trButton.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent event) {
                timer.schedule(new timertask(loginFrame), 0, 1000*30*loginFrame.getti());//时间间隔30秒
            }
        });

public class timertask extends TimerTask{
    
    private LoginFrame loginFrame;
    
    public timertask(LoginFrame loginFrame) {
        // TODO Auto-generated constructor stub
        this.loginFrame = loginFrame;
        }

    public void run(){
        
        GetcThread getcthread = new GetcThread(loginFrame);
        Thread t = new Thread(getcthread);
        t.start();
    }
}

public class Test {

    public static void main(String[] args) {
        try {
            ThreadTest tt = new ThreadTest();
            ThreadTest.flag = true;
            new Thread(tt).start();
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        ThreadTest.flag = false;
        
        try {
            Thread.sleep(1000);
            ThreadTest tt1 = new ThreadTest();
            ThreadTest.flag = true;
            new Thread(tt1).start();        
        } catch (InterruptedException e) {
            e.printStackTrace();
        }        
    }

}

class ThreadTest implements Runnable{
    
    public static boolean flag = false;

    public void run(){
        while(flag){
            try {
                Thread.sleep(100);
                System.out.println(Thread.currentThread() + "is running.");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            
        }
    }
}

------解决方案--------------------

关闭旧线程后，最好判断下旧线程是否已结束工作状态来决定创建新线程的时机
Thread::isAlive()  Thread::getState() ...