Java Program for number conversions

The following code is to convert the number i.e., Decimal Number to either Binary or Octal or Hexadecimal Number according to user's choice.
Code:-

import java.util.*;
public class Convert {
    Scanner scan = new Scanner(System.in);
    int choice, dev;
    String r = "\0";
    long num, res, rem, temp;
    public void input() {
        try {
            System.out.printf("1: Decimal to Binary\n2: Decimal to Octal\n3: Decal to Hexadecimal\nEnter your choice: ");
            choice = scan.nextInt();
            System.out.printf("Enter number: ");
            num = scan.nextLong();
        } catch (NumberFormatException | InputMismatchException e) {
            System.err.println("Error Occur!\n" + e.getMessage());
            System.exit(0);
        }
    }
    public void compute() {
        switch (choice) {
            case 1:
                dev = 2;
                break;
            case 2:
                dev = 8;
                break;
            case 3:
                dev = 16;
                break;
            default:
                System.err.println("Invalid Choice!");
                System.exit(0);
        }
        temp = num;
        char cha;
        while (temp != 0) {
            rem = temp % dev;
            temp /= dev;
            if (rem < 10) {
                r = r.concat(Long.toString(rem));
            }
            if (rem > 9) {
                cha = hexadecimal(rem);
                r = r.concat(Character.toString(cha));
            }
        }
        StringBuffer str = (new StringBuffer(r)).reverse();
        r = str.toString();
        System.out.println("Converted Number: " + r);
    }
    public char hexadecimal(long re) {
        char cha;
        if (re == 10) {
            cha = 'A';
        } else if (re == 11) {
            cha = 'B';
        } else if (re == 12) {
            cha = 'C';
        } else if (re == 13) {
            cha = 'D';
        } else if (re == 14) {
            cha = 'E';
        } else {
            cha = 'F';
        }
        return cha;
    }
    public static void main(String[] args) {
        Convert con = new Convert();
        con.input();
        con.compute();
    }
}

Output:-
1: Decimal to Binary
2: Decimal to Octal
3: Decal to Hexadecimal
Enter your choice: 3
Enter number: 50
Converted Number: 32