Java program to check given number is goldbach number or not

A Goldbach number is a positive even integer that can be expressed as the sum of two odd primes. Note: All even integer numbers greater than 4 are Goldbach numbers. Example: 6 = 3 + 3, 10 = 3 + 7, 10 = 5 + 5 Hence, 6 has one odd prime pair 3 and 3. Similarly, 10 has two odd prime pairs, i.e. 3 and 7, 5 and 5.

Write a program to accept an even integer ‘N’ where N > 9 and N < 50. Find all the odd prime pairs whose sum is equal to the number ‘N’.

Test your program with the following data and some random data:

Example 1: INPUT: N = 14

OUTPUT: PRIME PAIRS ARE: 3, 11 7, 7

Example 2: INPUT: N = 30

OUTPUT: PRIME PAIRS ARE: 7, 23 11, 19 13, 17

Example 3: INPUT: N = 17

OUTPUT: INVALID INPUT. NUMBER IS ODD.

Example 4: INPUT: N = 126

OUTPUT: INVALID INPUT. NUMBER OUT OF RANGE.

import java.util.*;
class Goldbach
{
    static boolean isPrime(int num)
    {
        int flag=0,a;
        for(a=2;a<=num/2;a++)
        {
            if(num%a==0)
            {
                flag=1;
                break;
            }
        }
        if (flag==0 && num>1)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
    public static void main(String arr[])
    {
        Scanner sc=new Scanner(System.in);
        System.out.println("Enter any Number : ");
        int n=sc.nextInt();
        if(n<=9||n>=50)
        {
            System.out.println("INVALID INPUT. NUMBER OUT OF RANGE.");
        }
        else if(n%2!=0)
        {
             System.out.println("INVALID INPUT. NUMBER IS ODD.");
        }
        else
        {
            for(int a=1;a<=n/2;a++)
            {
                if(Goldbach.isPrime(a) && Goldbach.isPrime(n-a))
                {
                    System.out.print(a+","+(n-a)+"\t");
                }
            }
        }
    }
}

Enter any Number : 

30

7,23 11,19 13,17