Tribonacci

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 *
 *
 */
public class Tribonacci {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
        try {
            System.out.print("Please Enter a number :");
            Integer n = Integer.parseInt(bf.readLine());

            if(n < 0){
                throw new NegativeNumberException("Negative Numbers are not allowed!!");
            }
            else if(n > 0 && n < 4){
                throw new InvalidInputException("You must not enter a valid input above 4");
            }
            else{
                int a=0,b=1,c=1,sum=0;
                System.out.print("The Tribonacci Serices is :\n 0\t 1\t 1\t");
                while(n > 3){
                    sum = a+b+c;
                    System.out.print(sum +"\t");
                    n--;
                    a = b;
                    b = c;
                    c = sum;
                }
            }
        }catch (NumberFormatException e) {
            // TODO Auto-generated catch block
            System.out.print("Please enter Numbers only !!");
        } catch (NegativeNumberException e){
            System.out.print(e.getMessage());
        }catch (InvalidInputException e){
            System.out.print(e.getMessage());
        }
        catch (IOException e) {
            // TODO Auto-generated catch block
            System.out.print("Unexpceted error !!");
        }


    }

}

class InvalidInputException extends Exception{
    private static final long serialVersionUID = 1L;

    public InvalidInputException(String msg){
        super(msg);
    }

}