Computer Science 252
Problem Solving with Java

Spring 2015, The College of Saint Rose

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Agenda

• Announcements
  • Lab 7: Bouncy GUI Ball continues, due Sunday night (though I hope you still finish sooner)
• Exam 2 comes out next Tuesday (3/24)
  • you will receive a PDF by email so be sure to check that morning
  • this is a take-home lab practical exam
  • you will be asked to write and/or modify programs
  • topics up to GUI, not recursion
  • if you understand the class examples and have done the in-class and lab exercises, you will have no problem with the problems
  • there will be 4 problems:
    1. "how do I draw that?" where you are given a picture and description and have to write the program to draw it
    2. a custom object problem along the lines of the "fun with flags" program you had on the first exam (except this time you will type it in and run it)
    3. a program where you add animation capabilities to a program
    4. a program that has some inappropriate variable declarations that you will be in charge of fixing
  • due by 9 AM Thursday
• Lab 6: Furious Fowl recap
• Recap of some of the key ideas we have seen that come up frequently
  • persistence of data: what needs to be an instance variable and what should not
  • custom classes: teach Java about a new kind of object - how to create it and how it answers questions (its accessors) and obeys commands (its mutators)
  • information flow within a program
    • instance variables to share information among methods of a given object (instance of a class)
    • method calls and their parameters and return values to share information among objects
• More recursion
  • more methods of a recursive structure
  • non-graphical recursive methods

Lecture 16 Assignment

Due at the start of class, Thursday, March 19.

Please submit answers to these questions in Submission Box under "LA16" or in hard copy by the start of our next class. We will discuss these questions at the start of class, so no late submissions are accepted. Please be sure that your name is clearly indicated in all submissions.

For this lecture assignment, you will be writing a Java application - a program that is not in a WindowController class but instead has a main method that does its work. It will be similar in structure to the Powers example. Write your program in Factorial.java. As in that example, you will need to create a keyboard Scanner to read in a number from the terminal and use System.out.println to issue a prompt and report your answer.

The problem we are going to solve is that of computing factorials. From math, you know that the factorial of a positive integer n, denoted n!, is the product of all the numbers from 1 up to n.

• Write a main method of your Factorial class that prompts for and reads in a positive integer. You need not worry about error checking the input for this assignment. (2 points)
• Write an iterative method loopFactorial that takes a single int as its parameter and returns the factorial of that value. Recall that an iterative method uses loop structures like for and while loops to do its work. Also update your main method to call the loopFactorial method on the number entered by the user, and print out the value returned. (4 points)
• Write a recursive mathematical formulation, along the lines of the second power formula in the notes, for computing n!. (2 points)
• Write a recursive method recFactorial that uses that formulation to compute factorials. Also update your main method to call the recFactorial method on the number entered by the user, and print out the value returned. (6 points)

Terminology

• base case
• recursive case

Examples

• NestedSquaresSizes
• Powers