Class 21: Recursion

Held Thursday, September 30, 1999

Overview

Today, we will ground our learning of recursion in Java by experimenting with two recursive functions, one that computes Fibonacci numbers and one that does exponentiation. In each case, we will consider both inefficient and more efficient versions.

Notes

• Don't forget tomorrow's talk!
• Note that you should not start today's lab with A1.1. Instead, skip to problem A1.3.
• Don't forget today's cool convocation talk.

Contents

• Lab
• Recursion

Handouts

• Lab A1

Summary

• Today:
  • Lab A1; Recursion
• Short discussion:
  • Recursive functions
• Assigned (for tomorrow):
  • Lab A2: Searching

Lab

Do A1.3 and A1.4.

Recursion

• You've studied Scheme, so you should know about recursion.
  • As you've observed, it's not much different in Java.
• A recursive function is a function which calls itself, either directly or indirectly.
  • A function calls itself indirectly by calling another function which calls the original function.
• Recursion provides one mechanism for looping.
• Many mathematicians and computer scientists consider recursion significantly more elegant than for or while loops.
• The body of a typical recursive function looks like

  if (some-test) {
    base-case;
  } // base case
  else {
    call-the-same-function-again-with-modified-parameters;
  } // recursive case