在 Throttle 类旁边使用扫描仪

Question

我有一个项目，我们使用了 Throttle 类和 MainClass。我们现在必须创建一个新的 while 循环，提示用户使用扫描仪输入从 0 到 6 的位置数据。

当用户输入-1时，代码需要退出。我只是在实现具有节流级别的扫描仪时遇到问题。我可以不使用 Throttle 类，但这不是作业。

完整说明（复制和粘贴）：

• 通过删除 while 循环来修改 MainClass。
• 创建一个新的 while 循环，提示用户使用扫描仪输入位置数据。
• 当用户输入-1时，代码将退出。

用户应输入0到6之间的位置。除-1外，数据必须在0到6之间；所有其他数据均应被忽略。用户每次输入有效位置，流量都会重新计算并显示。

这是主类：

package Pck1;

public class MainClass {

    public static void main(String[] args) {
        int position = 3;
        //position is used in-case of using something different from 3
        Throttle throttle = new Throttle(position);
        
        while (throttle.is_on())
        {
            System.out.println("The throttle is on." + "flow = " 
                    + throttle.flow());
            throttle.shift(-1);
        }
            System.out.println("The throttle is off." );
        }
}

这里是油门类别：

package Pck1;

public class Throttle {

    // Data Members
    private int position;
    // Constructors
    public Throttle(int position) {
    this.position = position;
    }
    // Membership Functions
    public boolean is_on() {
    return flow() > 0;
    }
    
    public double flow() {
    return position / 6.0;
    }
    
    public void shift(int amount) {
    position += amount;
    
    if (position < 0)
    position = 0;
    else if (position > 6)
    position = 6;
    }
    
    public void shut_off() {
    position = 0;
    }
}

我尝试了以下方法，但我知道它很糟糕。

package Pck1;

import java.util.Scanner;

public class MainClass {
    public static void main(String[] args) {
    
    int j = 0;
    
    Scanner input =  new Scanner(System.in);
    System.out.println("Enter speed between 0 and 6: ");
        j = input.nextInt();


        Throttle throttle = new Throttle(j);
        
          while(j > 6){

                j = input.nextInt();//read input from user
                System.out.println();

                if (j >=0 && j <=6 ) {
                    System.out.println("Validated input: " + j);
                    input.close();          
                }//end if statement

                else {
                    System.out.println("Enter a number between 1 and 6");
                    j = input.nextInt();
                }//end else statement

            }//end while loop       

            }//end main method

        }//end class

Answer 1

需要注意的是，我对 Java 的经验并不丰富，这里有一个满足说明的选项（带有一些注释来解释实现）。

从根本上来说，我认为这个分配是错误的：你的

Throttle

类没有方法直接操纵油门位置；您只能向上或向下移动相对数量。提示用户输入正数或负数，然后将其提供给

Throttle.shift

方法会更有意义；或者，如果

Throttle

类具有类似

setPosition

方法之类的东西，则此分配也会更明智。事实并非如此，这意味着完成指令的唯一方法是创建一个新的

Throttle

实例来响应用户的每个输入。这完全是废话。

无论如何，给你：

package Pck1;

import java.util.Scanner;

public class MainClass {
    /**
     * Prompt the user for a new Throttle position. This routine will
     * loop until the user enters valid data, re-prompting the user each
     * time.
     */
    private static int readPosition(Scanner input) {
        int position;

        // Keep prompting until we get valid input.
        while (true) {
            System.out.print("Enter throttle position (0-6); enter -1 to quit: ");
            try {
                position = input.nextInt();
                if (position >= -1 && position <= 6)
                    // Exit the loop if we have valid data.
                    break;
            } catch (java.util.InputMismatchException e) {
                /**
                 * We end up here if the user enters a non-integer response.
                 * This call discards the invalid token so that we can try
                 * reading new input.
                 */
                input.next();
            }

            /**
             * If we get here, the user entered invalid data. Either they entered
             * a number that it out of range, or they entered some non-numeric
             * response. In either case, display an error and re-prompt.
             */
            System.out.println("Invalid input.");
        }

        return position;
    }

    public static void main(String[] args) {
        Throttle throttle;
        Scanner input =  new Scanner(System.in);

        /**
         * This is a try-with-resources [1] statement; it ensures that we properly
         * close the scanner when we exit the try block. That's not strictly necessary
         * in this code, but it stops my IDE from complaining about the unclosed scanner.
         *
         * [1]: https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html
         */
        try (input) {
            while(true) {
                int position = readPosition(input);

                if (position == -1) {
                    // Exit if user enters -1.
                    break;
                } else {
                    // Otherwise create a new Throttle with updated position.
                    throttle = new Throttle(position);
                }

                System.out.println("Flow is now: " + throttle.flow());
            }
        }
    }
}