18.6. Recursion vs. Iteration

We’ve studied methods factorial and fibonacci, which can easily be implemented either recursively or iteratively. In this section, we compare the two approaches and discuss why you might choose one approach over the other in a particular situation.

Both iteration and recursion are based on a control statement: Iteration uses a repetition statement (e.g., for, while or do...while), whereas recursion uses a selection statement (e.g., if, if...else or switch). Both iteration and recursion involve repetition: Iteration explicitly uses a repetition statement, whereas recursion achieves repetition through repeated method calls. Iteration and recursion each involve a termination test: Iteration terminates when the loop-continuation condition fails, whereas recursion terminates when a base case is reached. Iteration with counter-controlled repetition and recursion both gradually approach termination: Iteration keeps modifying a counter until the counter assumes a value that makes the loop-continuation condition fail, whereas recursion keeps producing smaller versions of the original problem until the base case is reached. Both iteration and recursion can occur infinitely: An infinite loop occurs with iteration if the loop-continuation test never becomes false, whereas infinite recursion occurs if the recursion step does not reduce the problem each time in a manner that converges on the base case, or if the base case is not tested.