Java · Theory

Recursion in Java

Theory

63/270

Recursion in Java

Recursion is a method calling itself. Write the base case first: if (n <= 1) return 1; then the step: return n * fact(n - 1);. No base case → StackOverflowError.

Trace fact(5) on paper: 5*4*3*2*1. Recursion uses the call stack. Deep recursion can blow memory. Some problems are clearer as loops.

Use recursion when the problem is the same shape smaller: factorial, tree walk, simple Fibonacci demo.

Let's take this on the board with one tiny Main class — no extra files. Recursion in Java — output: 120. fact(5) → 5*fact(4) → … → 5*4*3*2*1. Stop when n <= 1. Start from main, go line by line, and stop at each print. That output is the proof for Recursion.

Exam tip

Say base case first, then the recursive step. Trace fact(5).

Example

public class Main {
  static int fact(int n) {
    if (n <= 1) return 1;
    return n * fact(n - 1);
  }
  public static void main(String[] args) {
    System.out.println(fact(5)); // 120
  }
}

Recursion in Java — output: 120. fact(5) → 5*fact(4) → … → 5*4*3*2*1. Stop when n <= 1.

Short notes

DefRecursion = method calls itself until a base case.
RuleBase case first. No base → StackOverflowError.
Usefactorial, tree, self-similar problems.
RememberTrace one tiny input on paper before coding.

Java · Theory

Recursion in Java

← All stacks

Theory

63/270

Recursion in Java

Recursion is a method calling itself. Write the base case first: if (n <= 1) return 1; then the step: return n * fact(n - 1);. No base case → StackOverflowError.

Trace fact(5) on paper: 5*4*3*2*1. Recursion uses the call stack. Deep recursion can blow memory. Some problems are clearer as loops.

Use recursion when the problem is the same shape smaller: factorial, tree walk, simple Fibonacci demo.

Exam tip

Say base case first, then the recursive step. Trace fact(5).

Example

public class Main {
  static int fact(int n) {
    if (n <= 1) return 1;
    return n * fact(n - 1);
  }
  public static void main(String[] args) {
    System.out.println(fact(5)); // 120
  }
}

Recursion in Java — output: 120. fact(5) → 5*fact(4) → … → 5*4*3*2*1. Stop when n <= 1.

Short notes

DefRecursion = method calls itself until a base case.
RuleBase case first. No base → StackOverflowError.
Usefactorial, tree, self-similar problems.
RememberTrace one tiny input on paper before coding.

Recursion in Java

Example

Short notes

Questions

Recursion in Java

Example

Short notes

Questions