Using the same method declared in the method?

Question

So been studying for my past exam and come across this question which asks what will the return value be if num = 7? Plugging it into BlueJ tells me 16, what does the func1 do to make it 16? How can the method declared be used again within the method? I searched but hard to find this exact example as it all comes up with just using methods normally.

Thanks,

public int func1(int num) 
{
  if ( num <= 2 ) return 1;
  return func1(num – 2) + num;
}

Answer 1

That is a recursive call to the same function you are using it in.

So, func1(num – 2) will invoke the same function - public int func1(int num) with num = num - 2, until num >= 2

So, you recursion goes like this: -

func(n)
   calls func(n-2)
      calls func(n-4)
         .. so on
         calls func(1)
            returns 1
         returns 1 + 3 + ... + (n - 4)
      returns 1 + 3 + ... + (n - 4) + (n - 2) 
   returns 1 + 3 + ... + (n - 4) + (n - 2) + n

UPDATE: - Generalized the above recursion, to let you figure out how it works.

You can go through: - Recursion - Wiki Page