如何验证范围内的用户输入？和 For 循环问题/混乱

如何解决如何验证范围内的用户输入？和 For 循环问题/混乱

当您输入年份时，我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，然后在我需要代码打印出它刹车/减速 3 次之后。我有一个 Java 类和一个 Java 主类。我尝试实施一种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.*;

公开课 MotorcycleDemo {

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 次并刹车 3 次，则输出应显示：“A year 和 make（摩托车品牌） is going speed mph。从速度 0 mph 开始，达到最大速度 20，然后减速 4 次，最终 速度 达到 5 mph。

感谢任何帮助并提前致谢。 :)

解决方法

然后尝试围绕您的输入处理设置一个 while/do-while 循环。如果输入不正确，则通过将布尔值设置为与 while 条件相同来保持循环运行，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);

        }
    }