Return statement

We have to print something in return statement like return 0 or return c .There was a problem in geeks for geeks to print all subsequence string in that problem they just wrote return and got the output. How is it possible ?

This is a code from geeks for geeks-

// Java program for the above approach
import java.util.*;
class GFG {

// Declare a global list
static List<String> al = new ArrayList<>();

// Creating a public static Arraylist such that
// we can store values
// IF there is any question of returning the
// we can directly return too// public static
// ArrayList<String> al = new ArrayList<String>();
public static void main(String[] args)
{
	String s = "abcd";
	findsubsequences(s, ""); // Calling a function
	System.out.println(al);
}

private static void findsubsequences(String s,
									String ans)
{
	if (s.length() == 0) {
		al.add(ans);
		return;
	}

	// We add adding 1st character in string
	findsubsequences(s.substring(1), ans + s.charAt(0));

	// Not adding first character of the string
	// because the concept of subsequence either
	// character will present or not
	findsubsequences(s.substring(1), ans);
}

}