How to get a specific type of exception in Java

I am trying to get a specific exception

Input H=-1; B=2;

Expected Output

java.lang.Exception: Breadth and height must be positive

Current Output

-2

public class Solution {
static int H,B;
static boolean flag = true;
static                                         //static initializer block
{
    
    Scanner sc = new Scanner(System.in);
    H=sc.nextInt();
    B=sc.nextInt();
    
}

public static void main(String[] args){
        if(flag){
            int area=B*H;
            System.out.print(area);
        }
        
    }

}

How do I get that specific exception?

You can throw your own exception like this

if(H<0 || B<0){
 throw new Exception("Breadth and height must be positive");
}

However, it would be a better practice to use something like a IllegalArgumentException for this.

if(H<0 || B<0){
 throw new IllegalArgumentException("Breadth and height must be positive");
}