如何用另一种方法停止正在运行的方法？

Question

所以这是我的大学作业，我几乎完成了所有工作。它应该使用方法覆盖，我必须从我的教授的课程（我不能改变任何东西）RidingMower 扩展我的课程 SafeRidingMower（将在解释后插入代码）。

RidingMower 类：

    import java.util.*;

/**
 * The riding mower class developed by the engineering department. Contains all the functionality needed
 * for a working riding mower.
 *
 */
public class RidingMower {

    private boolean rider_in_seat = false;

    private boolean is_engine_on = false;

    private boolean is_mower_enabled = false;

    private Random rn = new Random();

    /**
     * Constructor for Riding Mower which automatically launches the main menu.
     */
    public RidingMower()
    {
        mainMenu();
    }

    /** Starts the engine of the riding mower (ignition start) */
    public void start_engine()
    {
        System.out.println("<<< Starting riding mower >>>");

        is_engine_on = true;
    }

    /** Method that randomly seats and unseats a driver */
    private void sit_rider()
    {

        int random = rn.nextInt(5);

        if ( random<=1 )
             rider_in_seat = true;
        else rider_in_seat = false;       

        System.out.print("\t=>Seated? " + rider_in_seat + "\n");
    }

    /** Seat sensor. Returns true if there is a driver seated on the mower or false
     * if no driver is sitting on the mower.
     * @return 
     */
    public boolean check_seat_sensor()
    {   
        return rider_in_seat;
    }

    /** Method that engages the mower blades and begins mowing if the ignition is turned on */
    public void mow()
    {
        start_mowing();
    }

    /** Primary method that handles the mowing. Checks to see if the ignition is on then the 
      mowing starts otherwise the cutting blades are lowered and ready to mow upon engine start
      */
    private void start_mowing()
    {

        is_mower_enabled = true;

        System.out.println("Mower blade ready to mow");

        if ( !is_engine_on ) return;

        int i=1;

        while (true)
        {
            mowing(i++);

        }
    }

    /** Mower fully functioning here and blades are spinning. Simulates a rider being thrown off 
     the mower at step 50,000 */
    private void mowing(int i)
    {
        System.out.println( "Mowing..." + i);

        if ( i>50000 ) rider_in_seat = false;

        if ( rider_in_seat == false )
            System.out.println("\tOMG Mower is moving without a driver?!");

        mowing_hook();
    }

    /** Hook/Stub function called while the mower is mowing. Other departments divisions can override */
    public void mowing_hook()
    {

    }

    /** Turns off the ignition. Stops the mower if running. */
    public void stop_mower()
    {
        System.out.println("Stopping the mower.");
        System.exit(0);
    }

    /** Main menu of the mower simulation. Asks user to check/seat a driver, start the mower, 
     * begn mowing the lawn, or exiting the simulation. Method is private and can not be 
     * overriden.
     */
    private void mainMenu()
    {
        Scanner sc = new Scanner( System.in );
        int option;

        do
        {
            System.out.println();
            System.out.println("1. Is driver seated? (" + rider_in_seat +")" );
            System.out.println("2. Start mower");
            System.out.println("3. Mow the lawn");
            System.out.println("4. Stop mower (if running) and Exit.");
            System.out.println();
            System.out.println("CHOOSE 1-4");

            option = sc.nextInt();

            switch ( option )
            {        
                case 1: sit_rider();
                        break;

                case 2: start_engine();
                        if ( is_mower_enabled ) mow();
                        break;

                case 3: mow();
                        break;

                case 4: stop_mower();
                        break;
            }

        } while ( true ); // Infinite loop here. Select option #4 to exit the program.
    }
}

SafeRidingMower 类：

public class SafeRidingMower extends RidingMower 
{

    @Override
    public void start_engine() {
        if (check_seat_sensor() == true)
            super.start_engine();
        else
            System.out.println("Seat sensor does not detect a driver."
                    + "Engine will not start.");
    }

    @Override
    public boolean check_seat_sensor() {
        return super.check_seat_sensor();
    }

    @Override
    public void mow() {
        if (check_seat_sensor() == true)
            super.mow();
        else if (check_seat_sensor() == false)
            System.out.println("Seat sensor does not detect a driver."
                    + " Mower will not start.");
        else
            System.out.println("Engine is not on. Cannot start mowing.");
    }

    @Override
    public void mowing_hook() {

    }
}

还有驱动程序，我认为它与我遇到的特定问题无关，但无论如何都是这样。

public class TheLawnMowerManDriver {

public static void main(String[] args)
{

    RidingMower mower = new SafeRidingMower();

}

}

我需要做的：在 RidingMower 类中，有一个我无法覆盖的方法 mowing()，但我可以覆盖在方法 mowing() 结束时调用的方法 mowing_hook()。我应该做的是在变量 i = 50000 时停止割草机运行，但我不知道该怎么做。我尝试将 super 关键字与变量一起使用，但它不起作用（我不知道它是否应该起作用，我只是在几节课前才接触到 super 关键字）。

有谁知道我可以停止割草机/停止变量 i 从覆盖 mowing_hook() 方法计数的方法？

Answer 1

我找到了解决这个问题的方法。

正如我所说，我相信或者你误解了这个问题，或者你的教授在欺骗你。

无论如何，如果我们观察mowing()方法执行indirectly，是可以停止执行的。

这个想法是包装 System.out 并记录最后打印的字符串。因此，在mowing_hook() 中，我们可以看到手表已打印并在必要时停止。

您可以在此处找到一个工作示例：jdoodle.com/a/12KZ

总结：

将此类添加到您的代码中

class SystemOutWrapper extends PrintStream{
    String lastLine;

    public SystemOutWrapper(OutputStream out){
        super(out);
    }

    @Override
    public void println (String str){
        this.lastLine = str;
        super.println(str);
    }

    public String getLastLine(){
        return lastLine;
    }
}

并以这种方式覆盖该方法

@Override
public void mowing_hook() {

    if (! (System.out instanceof SystemOutWrapper)){
        System.setOut(new SystemOutWrapper(System.out));
    }

    //I used 100 as the online editor limitation. But you should change to 50000
    if ("Mowing...100".equals( ((SystemOutWrapper) System.out).getLastLine())){
        System.out.println("Limite reached! Should stop now!");
        stop_mower();
    }
}

Answer 2

一次：
1、i是方法mowing()的局部变量和；
2.方法mowing()不要将i的值传递给方法mowing_hook()

所以，在方法@​​987654327@中读取i的值是不可能的。

我有两个臀部：
1. 你的教授在骗你
2.你误解了作业

我会给出一些替代方案：

1. 更改方法mowing_hook()的签名

   /** Mower fully functioning here and blades are spinning. Simulates a rider being thrown off the mower at step 50,000 */
   private void mowing(int i)
   {
       System.out.println( "Mowing..." + i);
   
       if ( i>50000 ) rider_in_seat = false;
   
       if ( rider_in_seat == false )
           System.out.println("\tOMG Mower is moving without a driver?!");
   
       mowing_hook(i);
       }
   
       public void mowing_hook(int i)
       {
   
       }
   }
   

   并以这种方式覆盖

   @Override
   public void mowing_hook(int i) {
       if (i == 50000) stop_mower();
   }
   

2. 或者使用实例变量rider_in_seat

   @Override
   public void mowing_hook(int i) {
       if (!rider_in_seat) stop_mower(); 
   }
   

   但请注意，rider_in_seat 仅在 i > 50000 时才会设置为 false，因为 if ( i>50000 ) rider_in_seat = false; 行