如何用另一种方法停止运行方法？

Question

这是我的大学作业，我几乎完成了所有事情。它应该使用方法覆盖，我必须从我的 class SafeRidingMower（将在解释后插入代码）做，它从我教授的 class（我不能改变任何东西）RidingMower 延伸。

骑马割草机Class:

    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 Class:

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具体问题无关，但无论如何都在这里。

public class TheLawnMowerManDriver {

public static void main(String[] args)
{

    RidingMower mower = new SafeRidingMower();

}

}

我需要做的：在 RidingMower class 中，有一个我无法覆盖的 mowing() 方法，但我可以覆盖在mowing() 方法结束。我应该做的是在变量 i = 50000 时从运行停止割草机，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，我只是在几个 classes 之前才被介绍到 super 关键字）。

有谁知道我可以阻止 lawnmower/stop 变量 i 重写 mowing_hook() 方法的方法吗？

Answer 1

一次：
1. i 是方法的局部变量 mowing() and;
2.方法mowing()不把i的值传递给方法mowing_hook()

所以，在方法mowing_hook().

中读取不到i的值

我有两个hipotesis:
1. 你的教授在耍你
2. 你误解了作业

我会给出一些替代方案：

更改方法的签名mowing_hook()

/** 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();
}

或者使用实例变量rider_in_seat
```
@Override
public void mowing_hook(int i) {
    if (!rider_in_seat) stop_mower(); 
}
```
但是意识到只有在 i > 50000 时 rider_in_seat 才会被设置为 false，因为行 if ( i>50000 ) rider_in_seat = false;

Answer 2

我找到了这个问题的解决方案。

正如我所说，我相信或者你误解了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

想法是包装 System.out 并记录打印的最后一个字符串。因此，在 mowing_hook() 中我们可以看到 watch 已打印并在必要时停止。

您可以在这里找到一个工作示例：jdoodle。com/a/12KZ

总结：

将此 class 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();
    }
}

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