Reading and validating a number with Scanner

First of all, I have to say I'm quite new to Java.

I need to input a Double value using Scanner and need to check whether it is within the given range. If it's within the given range it should return the value, other开发者_开发问答wise it should ask to re-enter a new number

I tried my best, but there are compile errors. Please tell me how I should solve this in my code.

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);
        }
    }
}

---

Along with the comments regarding your val function not knowing what number is, it appears that the following is what you actually want your program to do:

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;
    }
  }
} 

---

A couple points:

1. The val function currently does not know of a variable called number. You want to pass the number value to the val function.
2. Since the val function has a returning type of String, it must return a String.

.

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

---

You can get rid of most of that code and do something like:

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();
}

Here's a complete program showing that snippet in action:

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: "));
    }
}

---

This is part a class I use. It's quite simple and it won't break if you enter a string. You can find more info about it here if you need it.

    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;
}