A recursive method calls itself with a smaller problem and must have a base case that stops. Without a base case the calls never end, and the program fails with StackOverflowError.
Factorial and a folder walk are natural recursive problems. A plain count from 1 to 10 is clearer as a loop. Use recursion when the data itself is nested.
Example
factorial(4) calls factorial(3), which calls factorial(2), which calls factorial(1). The base case returns 1, then each caller multiplies.
public class Fact {
static int factorial(int n) {
if (n <= 1) return 1;
return n * factorial(n - 1);
}
public static void main(String[] args) {
System.out.println(factorial(4));
}
}4 * 3 * 2 * 1 is 24. Keep the first recursive examples on small inputs. A deep chain uses one stack frame per call.
