Recursion Basics Java | Fresher Interview

Recursion is when a method calls itself to solve a problem by breaking it into smaller identical pieces. There are two essential parts you can't skip. First is the base case — that's your stopping condition. Without it, the function recurses forever and you get a StackOverflowError. Second is the recursive case, which is where you call the function again but with a smaller input that moves you closer to the base case. Let me give you factorial as an example. The base case is when n equals one or zero, you just return one. The recursive case is returning n times factorial of n minus one. So if you call factorial of five, it computes five times factorial of four, which computes four times factorial of three, and so on down to factorial of one. That's five stack frames deep. Once it hits the base case, the stack unwinds and each call returns its result back up. The key thing to understand is the call stack. Every recursive call creates a new stack frame with its own copy of the variables. Those frames pile up until the base case, then pop off as results return. That's why deep recursion can cause stack overflow in Java — the JVM has a limited stack size. The base case and the smaller recursive input should be checked together. For factorial(3), the calls must visibly progress through 3, 2, 1 and then stop before the stack unwinds.