A recursive method is a method that calls itself either
directly or indirectly
There are two key requirements to make sure
that the recursion is successful:
- Every recursive call must simplify the computation in some
- There must be special cases to handle the simplest
Iteration Vs. Recursion
- If a recursive method is called with a base case, the
method returns a result. If a method is called with a more complex problem,
the method divides the problem into two or more conceptual pieces: a piece
that the method knows how to do and a slightly smaller version of the
original problem. Because this new problem looks like the original problem,
the method launches a recursive call to work on the smaller problem.
- For recursion to terminate, each time the recursion method
calls itself with a slightly simpler version of the original problem, the
sequence of smaller and smaller problems must converge on the base case.
When the method recognizes the base case, the result is returned to the
previous method call and a sequence of returns ensures all the way up the
line until the original call of the method eventually returns the final
- Both iteration and recursion are based on a control
structure: Iteration uses a repetition structure; recursion uses a selection
- Both iteration and recursion involve repetition: Iteration
explicitly uses a repetition structure; recursion achieves repetition
through repeated method calls.
- Iteration and recursion each involve a termination test:
Iteration terminates when the loop-continuation condition fails; recursion
terminates when a base case is recognized.
- Iteration and recursion can occur infinitely: An infinite
loop occurs with iteration if the loop-continuation test never becomes
false; infinite recursion occurs if the recursion step does not reduce the
problem in a manner that converges on the base case.
- Recursion repeatedly invokes the mechanism, and
consequently the overhead, of method calls. This can be expensive in both
processor time and memory space.