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# Recursion in Java

Imagine you have a magic mirror. When you look into it, you see another mirror inside it, and inside that mirror, there's yet another mirror, and so on. That's a bit like recursion in Java!

In programming, recursion is like a mirror reflecting itself over and over until it reaches a stopping point. Let's say you want to count down from 5 to 1. Instead of using a loop, you can use recursion.

Here's how it works: You tell Java to count down from a number. Java counts down one number at a time, but then it remembers that it needs to count down again, starting from the next number. It's like having a little helper inside Java that keeps reminding it what to do next.

But here's the cool part: Recursion isn't just about counting down. It's like a superpower that lets you solve big problems by breaking them into smaller, more manageable pieces.

For example, think about a Russian nesting doll. It's a doll inside a doll inside a doll... You get the idea. Recursion works similarly. You can solve a big problem by solving a smaller version of the same problem, over and over again until you reach the simplest version.

## Program for recursion

java

```
public class FactorialCalculator {
public static int factorial(int n) {
// Base case: If n is 0 or 1, return 1
if (n == 0 || n == 1) {
return 1;
} else {
// Recursive case: n! = n * (n-1)!
return n * factorial(n - 1);
}
}
public static void main(String[] args) {
int number = 5;
int result = factorial(number);
System.out.println("Factorial of " + number + " is: " + result);
}
}
```

In our example, we have a `factorial()`

method that calculates the factorial of a given number. But here's where the magic happens—instead of using a loop, we call the `factorial()`

method within itself, gradually reducing the problem until we reach the base case.

As we traverse deeper into the realm of recursion, each invocation of the `factorial()`

method brings us closer to our goal, until finally, we reach the base case where n is 0 or 1. At this point, the recursion unwinds, and the factorial values are calculated and multiplied on the way back up the call stack.

But recursion isn't just about factorial calculations; it's a powerful tool for solving a wide range of problems, from traversing tree structures to searching through arrays and beyond.

java

```
public class RecursionExample {
public static void countdown(int n) {
if (n == 0) {
System.out.println("Blastoff!");
} else {
System.out.println(n);
countdown(n - 1); // Recursive call
}
}
public static void main(String[] args) {
countdown(5);
}
}
```

In our example, we have a method called `countdown()`

that takes an integer `n`

. If `n`

is equal to 0, we print "Blastoff!" and stop. Otherwise, we print the current value of `n`

and then make a recursive call to `countdown(n - 1)`

.

When we run the `main()`

method with an initial value of 5, here's what happens:

- We call
`countdown(5)`

. `countdown(5)`

prints 5 and then calls`countdown(4)`

.`countdown(4)`

prints 4 and then calls`countdown(3)`

.- This process continues until
`countdown(0)`

is called, printing "Blastoff!" and stopping.