Basic Exception Handling

package demo;
 // Basic exception handling

import java.util.Scanner;

public class HelloJava {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        int choice = 0;

        do{
            printMenu();
            choice = input.nextInt();

            if(choice == 1){
                handleReverse();
            }else if(choice == 2){
                handleAverage();
            }else if(choice == 3){
                handleLinearEquation();
            }else if(choice != 4){
                System.out.println("Invalid choice");
            }
        }while(choice != 4);

    }
    public static void handleLinearEquation(){
        Scanner input = new Scanner(System.in);
        System.out.print("Enter a, b and c");

        try{
            int a = input.nextInt();
            int b = input.nextInt();
            int c = input.nextInt();

            double[] roots = getRoots(a, b, c);
            if(roots[0] == roots[1] && roots[0] != 0){
                System.out.println(roots[0]);
            }else if(roots[0] == 0 && roots[1] == 0){
                System.out.println("No solution");
            }else{
                System.out.println(roots[0] + ", " + roots[1]);
            }
        }catch(Exception e){
            System.out.println("a can not be zero");
        }
    }

    public static double[] getRoots(int a, int b, int c) throws Exception{
        if(a == 0){
            throw new Exception();
        }
        double[] roots = {0, 0};

        double D = b * b - 4 * a * c;
        if(D > 0){
            roots[0] = (-b + Math.sqrt(D)) / (2 * a);
            roots[1] = (-b - Math.sqrt(D)) / (2 * a);
        }else if(D == 0){
            roots[0] = -b / (2 * a);
            roots[1] = roots[0];
        }

        return roots;
    }
    public static void handleAverage(){
        Scanner input = new Scanner(System.in);
        System.out.print("Enter numbers separated by space: ");

        try{
            String line = input.nextLine();
            String[] numbers = line.split(" ");

            double average = getAverage(numbers);
            System.out.println("Average: " + average);
        }catch(Exception e){
            System.out.println("You must enter at least one number");
        }
    }

    public static double getAverage(String[] numbers) throws Exception {
        if(numbers.length <= 0){
            throw new Exception();
        }

        double sum = 0;
        double average = 0;

        for(int i = 0; i < numbers.length; i++){
            sum += Double.parseDouble(numbers[i]);
        }

        average = sum / numbers.length;

        return average;
    }
    public static void handleReverse(){
        Scanner input = new Scanner(System.in);
        System.out.print("Enter number: ");

        try{
            int number = input.nextInt();
            int reversed = reverse(number);

            System.out.println("Reversed: " + reversed);
        }catch (Exception e){
            System.out.println("Number must be positive");
        }
    }

    public static void printMenu(){
        System.out.println();
        System.out.println("1. Reverse number");
        System.out.println("2. Get average from sequence");
        System.out.println("3. Solve linear equation");
        System.out.println("4. Exit");
    }
    public static int reverse(int n) throws Exception{
        if(n < 0){
            throw new Exception();
        }

        int rev = 0;
        int length = String.valueOf(n).length();

        if(length == 1){
            rev = n;
        }else{
            while(n != 0){
                length--;
                int lastDigit = n % 10;

                rev += lastDigit * Math.pow(10, length);
                n /= 10;
            }
        }

        return rev;
    }

}