Question

我试图在控制台中找到一个启动和停止无限循环的解决方案。

我最好的选择是什么？使用单独的线程或使用键事件侦听器？扫描仪可能是一种解决方案，但扫描仪等待输入......

boolean stop = false;
while(!stop){
    try {
            ...
        Thread.sleep(1000);
    } catch (InterruptedException e) {
        e.printStackTrace();
}

Answer 1

你需要一个无限循环包裹你的“可停止”循环。因为一旦你离开循环，你必须确保你可以再次输入它。

Answer 2

您可以将此部分放在方法中，并且首次默认调用此方法，然后包括事件侦听器，用于启动的特定键和用于停止循环的其他键。

Answer 3

这样的事情应涵盖所有情况：

import java.util.Scanner;
import java.util.logging.Logger;

public class Testclass {

    public static void main(String[] args) {

        final Logger logger = Logger.getLogger(Testclass.class.getName());

        /* Declare a scanner to get user input... */
        final Scanner scanner = new Scanner(System.in);

        /* ...and make sure it gets closed under all circumstances */
        Runtime.getRuntime().addShutdownHook(new Thread() {
            @Override
            public void run() {
                logger.info("Closing Scanner.");
                scanner.close();
            }
        });

        /* Our runnable which does the actual work */
        Runnable runner = new Runnable() {

            @Override
            public void run() {

                /* We want to run at least once */
                do {

                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        logger.info("Got interrupted");

                        /* Edit: we need to return here, as we don't want
                         * to execute the payload code in case
                         * we are interrupted. Replaces stopped variable
                         */
                         return;
                    }

                    /*
                     * Do here whatever you want.
                     */
                    logger.info("Doing Stuff");


                } while (true);
            }
        };

        /* We initialize to prevent ugly null checks */
        Thread t = new Thread(runner);

        /* You can actually enter whatever you want for stopping the thread */
        System.out.println("Enter \"s\" to start/stop thread, \"q\" to exit");

        while (true) {
            /* Blocking, our thread runs anyway if started */
            String input = scanner.next();

            if (!t.isAlive() && input.equals("s")) {

                /*
                 * We ensure that we have a new thread because stopped threads
                 * can't be reused.
                 */
                t = new Thread(runner);
                logger.info("Starting thread");
                t.start();

            } else if (t.isAlive()) {

                /*
                 * If the thread is alive, we want to stop it on user input
                 * regardless wether it is q or s
                 */
                logger.info("Shutting down thread...");

                /* We tell the thread to shut itself down */
                t.interrupt();

                try {
                    /* We wait for our thread to finish cleanly */
                    t.join();
                } catch (InterruptedException e) {
                    /* Something is severely wrong here */
                    logger.severe("Got interrupted during thread shutdown:");
                    e.printStackTrace();
                    logger.severe("Unclean exit!");
                    System.exit(5);
                }

                logger.info("Thread stopped");

            }

            /*
             * If the thread was running on user input
             * it is cleanly shut down by now
             * Next, we want to find out wether we should exit
             * or wait for the next user input of "s" to start.
             */
            if (input.equals("q")) {
                logger.info("Exiting...");
                System.exit(0);
            }
            /* Clear the input line */
            scanner.nextLine();

        }
    }
}

启动和停止无限循环

3 个答案: