improper inputs

i am working on a triangle detecting program, that is supposed to take in 3 user inputs for the length of the sides

to ensure that the program doesnt crash or anything, our teacher asked us to put in a loop or something to make sure that every time the user inputs a number less than 0 or any letters, the program is supposed to ask them for a proper input

so i am able to get the users to input a number greater than 0 but the problem i am having is that i cant figure out a way to stop them from entering in any letters

Code:

---

import java.util.Scanner;
  public class Triangle
  {
      public static void main (String [] args)
      {
        Scanner reader = new Scanner (System.in);
       
        double a;
        double b;
        double c;
        double largest;
        double middle;
        double smallest;
     
     
        System.out.print("Please enter the length of side #1: ");
        a = reader.nextDouble();
       
        while( a <= 0 )
        {
            System.out.println("");
            System.out.print("Please enter a number greater than zero: ");
            a = reader.nextDouble();
        }
       
        System.out.println("");
        System.out.print("Please enter the length of side #2: ");
        b = reader.nextDouble();
       
        while( b <= 0 )
        {
            System.out.println("");
            System.out.print("Please enter a number greater than zero: ");
            b = reader.nextDouble();
        }
       
        System.out.println("");
        System.out.print("Please enter the length of side #3: ");
        c = reader.nextDouble();
       
        while( c <= 0 )
        {
            System.out.println("");
            System.out.print("Please enter a number greater than zero: ");
            c = reader.nextDouble();
        }
       
        largest = Math.max(a,Math.max(b,c));
        smallest = Math.min(a,Math.min(b,c));
        middle = a + b + c - largest - smallest;
             
        if ((Math.pow(smallest,2) + Math.pow(middle,2) == Math.pow(largest,2)))
        {
            System.out.println("");
            System.out.println("It is a right triangle.");
        }
       
        else
        {
            System.out.println("");
            System.out.println("It is not a right triangle.");
        }
         
        if (a == b && a == c && b == c)
        {
            System.out.println("");
            System.out.println("It is an equilateral triangle.");
        }
               
        else if (a == b || a == c || b == c)
        {
            System.out.println(""); 
            System.out.println("It is an isosceles triangle.");
        }
                       
        else if (a != b && a != c && b != c)
        {
            System.out.println("");     
            System.out.println("It is an scalene triangle.");
        }
      }
  }

---

I am not sure but I would write:

Code:

---

if(!a.contains("1") |! a.contains("2") |!a.contains("3") |!a.contains("4") |!a.contains("5") |!a.contains("6") |!a.contains("7") |!a.contains("8") |!a.contains("9")){
System.out.println("Use only numbers please");
} else {

//put all your code in here from the line 19 to 46 and do the same for the others
}

---

Oh wait, my code is wrong xD hold on a minute..

Ok there is easier way:

Code:

---

if (a.matches("[0-9]+")) {
                        //if it has ONLY NUMBERS
                } else {
                        //has at least 1 non-number
                }

---

Code:

---

if(!a.contains("1") |! a.contains("2") |!a.contains("3") |!a.contains("4") |!a.contains("5") |!a.contains("6") |!a.contains("7") |!a.contains("8") |!a.contains("9")){

---

Arrrrrrrrrrgggggggggggh! My eyes.

A quick and dirty way is to read the input as a String, try parsing to int/double and catch exception. But since you are using the Scanner class try using the hasNext... methods.

Also, whenever you see repeated code you should be thinking about using a loop or a method.

Read my second post