如何验证范围内的用户输入？和循环 issue/confusion

Question

当您输入年份时，如何验证用户的输入，范围必须在 1900-2021 之间。我也对在我的情况下使用 for 循环感到困惑。我需要打印出摩托车加速四次，然后紧接着我需要代码打印出它 braking/deaccelerating 3 次。我有一个 java class 和一个 Java 主 class。我尝试实现一个单独的方法来验证年份，但最终导致程序崩溃。

public class Motorcycle {

private int year;
private String make;
private int speed;

/**
 * 
 * @param year
 * @param make 
 */
public Motorcycle(int year, String make) {
    this.year = year;
    this.make = make;
    this.speed = 0;
}
public Motorcycle(){
    this.year = 0;
    this.make = "";
    this.speed = 0;
}

public void setYear(int year) {
    this.year = year;
}

public void setMake(String make) {
    this.make = make;
}

public void setSpeed(int speed) {
    this.speed = speed;
}

public int getYear() {
    return year;
}

public String getMake() {
    return make;
}

public int getSpeed() {
    return speed;
}

public void accelerate() {
    this.speed += 5;
}

public void brake() {
    this.speed -= 5;
}

@Override
public String toString() {
    return "A " + year +" " + make + " going "+ speed +" miles per hour";



import java.util.*;

public class 摩托车演示 {

public static void main(String[] args) {
    int year;

    Scanner keyboard = new Scanner(System.in);

    System.out.println("Enter the year of your Motorcycle");  //validate year 1900 -2021 
    year = keyboard.nextInt();

    System.out.println("Enter the make of your Motorcycle(such as, Harley, Kawasaki)");
    String maker = keyboard.next();

    Motorcycle motor1 = new Motorcycle(year, maker);

    System.out.println(motor1); //account for 0 speed toString()
    for (int i = 0; i <= 3; i++) {            //use for loop  //accelerate 4 times and brake 3 times 
        motor1.accelerate();
        System.out.println(motor1);
        //System.out.println("A " + year + " " + maker + " going " + motor1.getSpeed() + "miles per hour.");
        //to String method     
    }
    for (int i = 0; i <= 3; i++);
    {

        motor1.brake();
        System.out.println(motor1);

    }

}

}

如果摩托车加速4次，刹车3次，那么输出应该显示："A year and make (motorcycle brand) 的速度为 speed mph。以 0 mph 的速度开始并达到 20 的最大速度，然后减速 4 次，最终 speed 为 5 mph。

感谢任何帮助，并提前致谢。 :)

Answer 1

然后尝试围绕您的输入处理设置一个 while/do-while 循环。通过设置一个与while条件相同的布尔值，如果输入不正确则保持循环运行，如果答案正确则跳出循环

    public static void main(String[] args) {

        int year;
        int currentYear = Calendar.getInstance().get(Calendar.YEAR); //Creating current year
        boolean looping = false;

        do {
            Scanner keyboard = new Scanner(System.in);
            System.out.println("Enter the year of your Motorcycle");  //validate year 1900 -2021
            year = keyboard.nextInt();

            if (year < 1900 || year > currentYear) {
                looping = true;
                System.out.println("Invalid year!\nPlease type in valid year!");
            } else
                System.out.println("Enter the make of your Motorcycle(such as, Harley, Kawasaki)");
                String maker = keyboard.next();
            //Put condition here too if necessary, and put looping true if input is bad
        } while(looping);  //As long as looping is set true it reruns form

        Motorcycle motor1 = new Motorcycle(year, maker);

        System.out.println(motor1); //account for 0 speed toString()
        for (int i = 0; i <= 3; i++) {            //use for loop  //accelerate 4 times and brake 3 times
            motor1.accelerate();
            System.out.println(motor1);
            //System.out.println("A " + year + " " + maker + " going " + motor1.getSpeed() + "miles per hour.");
            //to String method
        }
        for (int i = 0; i <= 3; i++);
        {

            motor1.brake();
            System.out.println(motor1);

        }
    }

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