說明：耗時任務開啟單獨執行緒處理，任務執行緒處理完畢通知主執行緒

1、回撥介面定義

public interface ResponseCallBack {
    public void printMsg(String msg);
}

2、模擬耗時任務執行緒

public class TestMain {

    public static void main(String[] args){
        ExecutorService executorService = Executors.newFixedThreadPool(1);
        executorService.submit(new TestThread(new ResponseCallBack() {
            @Override
            public void printMsg(String msg) {
                System.out.println("print message: " + msg);
            }
        }));
        executorService.shutdown();
    }
}

class TestThread implements Runnable {

    private ResponseCallBack responseCallBack;

    public TestThread(ResponseCallBack responseCallBack) {
        this.responseCallBack = responseCallBack;
    }

    @Override
    public void run() {
        try {
            System.out.println(Thread.currentThread().getName() + " start execute");
            Thread.sleep(3000);   // 耗時任務
            System.out.println(Thread.currentThread().getName() + " end execute");
            this.responseCallBack.printMsg("Hello Call Back");  // 耗時任務執行完後，通知主執行緒
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}