help with Scanner

[bvav22]

Hey guys, im trying to finish an assignment for a java class, and i have finished the program except for one part. The program requires that i take 3 values inputted from the user, the first 2 must be digits between 0 and 9, and the third an operator.
the operator decides if the two numbers are added subtracted...et c. anyways the things i cannot get, is i need to check if they enter valid digits, and not letters, however if i do put a letter in, scanner gives me an exception. it happens at line 14 when you enter a letter.... how can i test if it is a letter... any suggestions?


here is my code

import java.util.Scanner;
import java.text.DecimalFormat;
 
public class problem1 {
public static void main(String[]args){
 
    double num1,  num2, answ;
 
    String tString,num1Word = " ",num2Word= " ";
    Scanner scan = new Scanner(System.in);
    DecimalFormat formatter = new DecimalFormat("0");
 
    System.out.println("Please enter two numbers between 0 and 9 ");
    num1= scan.nextDouble();
    num2= scan.nextDouble();
 
    if(Character.isDigit((Double.toString(num1)).charAt(0))){
 
    }
    else{System.out.println("Please Enter Digits only!");
    System.exit(0);
    }
 
    switch((int)num1){
    case 0: num1Word= "Zero";
    break;
    case 1: num1Word= "One";
    break;
    case 2: num1Word= "Two";
    break;
    case 3: num1Word= "Three";
    break;
    case 4: num1Word= "Four";
    break;
    case 5: num1Word= "Five";
    break;
    case 6: num1Word= "Six";
    break;
    case 7: num1Word= "Seven";
    break;
    case 8: num1Word= "Eight";
    break;
    case 9: num1Word= "Nine";
    break;
    default: 
        System.out.println("Invalid Number");
    System.exit(0);
    break;
    }
    switch((int)num2){
    case 0: num2Word= "Zero";
    break;
    case 1: num2Word= "One";
    break;
    case 2: num2Word= "Two";
    break;
    case 3: num2Word= "Three";
    break;
    case 4: num2Word= "Four";
    break;
    case 5: num2Word= "Five";
    break;
    case 6: num2Word= "Six";
    break;
    case 7: num2Word= "Seven";
    break;
    case 8: num2Word= "Eight";
    break;
    case 9: num2Word= "Nine";
    break;
    default: 
        System.out.println("Invalid Number");
    System.exit(0);
    break;
    }
    System.out.println("Please enter the mathematical symbol for what you would like to do with these numbers. ");
    tString = scan.next();
    char operator = tString.charAt(0);
 
 
 
 
    switch(operator){
    case '*': answ= num1*num2;
        System.out.println(num1Word+ " Multiplied by "+num2Word+" is "+formatter.format(answ));
        break;
    case '/': if(num2 == 0){
        System.out.println("You cannot divide by zero, session terminated.");
 
    }
    else{
        answ= num1/num2;
        System.out.println(num1Word+ " Divided by "+num2Word+" is "+formatter.format(answ));
    }
    break;
    case '+': answ= num1 + num2;
    System.out.println(num1Word+ " Added to "+num2Word+" is "+formatter.format(answ));
    break;
    case '-': answ= num1 - num2;
    System.out.println(num1Word+ " Minus "+num2Word+" is "+formatter.format(answ));
    break;
    case '^': 
        answ= Math.pow(num1,num2);
    System.out.println(num1Word+ " raised to the power of " +num2Word+ " is "+ formatter.format(answ));
    break;
    default: System.out.println("Invalid Operator");
    System.exit(0);
    break;
    }
 
}
}
 

[horace1]

you can use method scanner.hasNext Double() to check if the next token can be read as a double and if not ignore it, e.g.

System.out.println("Please enter two numbers between 0 and 9 ");
while(!scan.hasNextDouble())
   { 
    System.out.printf("error, enter a double !"); 
    scan.nextLine();          // ignore rest of line
   }
num1= scan.nextDouble();
 

[bvav22]

i really cannot thank you enough, that was such a big help.... :)