Question

首先，我不得不说我对Java很新。

我需要使用Double输入Scanner值，并需要检查它是否在给定范围内。如果它在给定范围内，则应返回该值，否则应要求重新输入新数字

我尽我所能，但有编译错误。请告诉我如何在我的代码中解决这个问题。

class Find {

    public static void main(String args[]) {
        System.out.println(val(1, 100));
        Scanner input = new Scanner(System.in);
        double number;
        System.out.print("Enter a number: ");
        number = input.nextDouble();
    }

    private static String val(int minValue, int maxValue) {
        if (number < minValue || number > maxValue) {
            return "try again";
        } else {
            return (number);
        }
    }
}

Answer 1

几点：

val函数当前不知道名为number的变量。您希望将number值传递给val函数。
由于val函数的返回类型为String，因此必须返回String。

private static String val(double number, double minValue, double maxValue){
    if (number < minValue || number > maxValue ){
       return "try again";
   }
   else{
      return String.valueOf(number);
   }
}

Answer 2

除了有关val函数的评论不知道number是什么之外，以下是您实际希望程序执行的操作：

import java.util.Scanner;

class Find {

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

    do {
        System.out.print("Enter a number: "); 
        number = input.nextDouble();
    } while(!isValid(number));
  }

  private static boolean isValid(double number){
    int minValue = 1;
    int maxValue = 100;

    if (number < minValue || number > maxValue ) {
       System.out.println("Try again");
       return false;
    }
    else {
       return true;
    }
  }
}

Answer 3

您可以摆脱大部分代码并执行以下操作：

System.out.print( "Enter a number: " ); 
number = input.nextDouble();
while ((number < minValue) || (number > maxValue)) {
    System.out.println( "Number out of range." ); 
    System.out.print( "Enter a number: " ); 
    number = input.nextDouble();
}

这是一个完整的程序，显示了代码片段：

import java.util.Scanner;

public class Find {
    public static double getNum (
        double minVal,
        double maxVal,
        String prompt,
        String errPrompt
    ) {
        Scanner input = new Scanner(System.in);
        System.out.print (prompt); 
        double number = input.nextDouble();
        while ((number < minVal) || (number > maxVal)) {
            System.out.print (errPrompt); 
            number = input.nextDouble();
        }
        return number;
    }

    public static void main(String args[]) {
        System.out.println (getNum (1, 100, "Enter a number: ", "Try again: "));
    }
}

Answer 4

这是我使用的课程的一部分。这很简单，如果你输入一个字符串就不会破坏。如果需要，您可以找到有关它的更多信息here。

    public int readInt(String prompt, int min, int max)
{
    Scanner scan = new Scanner(System.in);

    int number = 0;

    //Run once and loop until the input is within the specified range.
    do 
    {
        //Print users message.
        System.out.printf("\n%s > ", prompt);

        //Prevent string input crashing the program.
        while (!scan.hasNextInt()) 
        {
            System.out.printf("Input doesn't match specifications. Try again.");
            System.out.printf("\n%s > ", prompt);
            scan.next(); 
        }

        //Set the number.
        number = scan.nextInt();

        //If the number is outside range print an error message.
        if (number < min || number > max)
            System.out.printf("Input doesn't match specifications. Try again.");

    } while (number < min || number > max);

    return number;
}   public int readInt(String prompt, int min, int max)
{
    Scanner scan = new Scanner(System.in);

    int number = 0;

    //Run once and loop until the input is within the specified range.
    do 
    {
        //Print users message.
        System.out.printf("\n%s > ", prompt);

        //Prevent string input crashing the program.
        while (!scan.hasNextInt()) 
        {
            System.out.printf("Input doesn't match specifications. Try again.");
            System.out.printf("\n%s > ", prompt);
            scan.next(); 
        }

        //Set the number.
        number = scan.nextInt();

        //If the number is outside range print an error message.
        if (number < min || number > max)
            System.out.printf("Input doesn't match specifications. Try again.");

    } while (number < min || number > max);

    return number;
}

使用Scanner读取和验证数字

4 个答案: