Why does return statement is throwing error when used Math function in a method

Question

Why does return statement is throwing error when used Math function in a method.

public class HCF_1 {
    
    static int hcf(int a, int b)
    {
        int res = Math.max(a,b);
        while(true)
        {
            if(res%a==0 && res%b==0)
                return res;
            else res++;
        }
        return res;
    }
    public static void main(String[] args) {
        
        System.out.println(hcf(5,25));
    }
}

It's unreachable. Replace the first `return` with `break`. Or delete the second `return`. — terrorrussia-keeps-killing, Nov 16 '20 at 19:02
Incidentally, once you fix the error, as per fluffy's advice, this won't give you the hcf; it'll give you the lcm. — Dawood ibn Kareem, Nov 16 '20 at 19:03
Does this answer your question? [Missing return statement in a non-void method compiles](https://stackoverflow.com/questions/16789832/missing-return-statement-in-a-non-void-method-compiles) — Charlie Armstrong, Nov 16 '20 at 19:09

score 2 · Answer 1 · edited Nov 16 '20 at 20:07

This may or may not be helpful, but IMO while(true) statements are a real code smell. You can rewrite this method as:

public class HCF_1 {
   
   static int hcf(int a, int b)
   {
       int res = Math.max(a,b);
       while(res % a != 0 || res % b != 0)
           res++;
       return res;
   }
   public static void main(String[] args) {
       System.out.println(hcf(5,25));
   }
}

Now there is only a single return statement, and no shortcuts.

Note that the operations !(res % a == 0 && res % b == 0) are the same as res % a != 0 || res % b != 0, due to to the properties of Boolean Logic: ~(A AND B) == ~A OR ~B.

score 0 · Answer 2 · answered Nov 16 '20 at 19:10

public class HCF_1 {
        
        static int hcf(int a, int b)
        {
            int res = Math.max(a,b);
            while(true)
            {
                if(res%a==0 && res%b==0)
                    return res;
                else res++;
            }
            return res; //last line of the method hcf is unreachable
        }
        public static void main(String[] args) {
            
            System.out.println(hcf(5,25));
        }
    }

The while loop is a never-ending loop and is escaped only under the condition mentioned inside if block which is a return statement and not a break statement. Therefore the last line of the method hcf return res; is unreachable in any condition.

score 0 · Answer 3 · answered Nov 16 '20 at 19:17

the segement of your code in if-else the cause to be unreachable for the last line of your return res, you so have to do 2 things:

remove the return inside if and add break instead.
return the last line of method which is return res;

public class HCF_1 {

    static int hcf(int a, int b) {
        int res = Math.max(a, b);
        while (true) {
            if (res % a == 0 && res % b == 0)
                break;
            else
                res++;
        }
        return res;
    }

    public static void main(String[] args) {

        System.out.println(hcf(5, 25));
    }
}

Why does return statement is throwing error when used Math function in a method

3 Answers3