Homework Assignment 2: Constructors and Command-line Arguments

Computer Science II (810:062)

Due: Friday, January 27, at 11:59 AM (noon)

Introduction

We have at least three different goals for this assignment:

• practice implementing constructors
• practice factoring common behavior into helper methods
• experience working with command-line arguments

For this homework, you will modify the MemoPadApp class to accept some optional command-line arguments. When running MemoPadApp, the possible command-line arguments that it will accept are:

Command-line Execution	Meaning
java MemoPadApp	Use the original DefaultMemoDatabase
java MemoPadApp -d	Use the original DefaultMemoDatabase
java MemoPadApp -s	Use your original student version of MyMemoDatabase from homework 1
java MemoPadApp -s 100	Use your MyMemoDatabase that is created by a new constructor that limits the database to the specified maximum size (in this example it is 100)

Here is a Java-specific items that might help you:

• Command-line arguments are always strings. Sometimes, though, we intend for the value to be treated as another type, say, an int. You can read about String conversions in the on-line documentation.

int integerValue = Integer.parseInt( stringValue );

You can pass any String that consists only of numeric characters to the method Integer.parseInt(), which returns the equivalent integer. For example, if stringValue is "100", integerValue will be given the value 100.

Tasks

Before starting, make a copy of MemoPad.java that you can use in later steps.

1. Add a new constructor to your MyMemoDatabase class that takes one argument: the maximum number of memos that can be stored.

Test your new constructor by using it to create the database in the MemoPad class and then running the program. Verify that the database enforces the maximum size!

Make sure that the class's default constructor still works, too, and that it still enforces its maximum number of entries.

1. Eliminate any code duplication in your MyMemoDatabase class's constructors.

Re-test both constructors by using them to create the database in the MemoPad class and then running the program.

1. Add a new constructor to the MemoPad class that takes one argument: the MemoDatabase that it uses to store the memos.

Test your new constructor by using it to create the MemoPad in the main() method and then running the program.

1. Change the original "default" constructor back to its original form, from before Homework 1: initialize the database variable to be a DefaultMemoDatabase.

1. Eliminate any code duplication in the MemoPad constructors.

Re-test both constructors by using them to create the MemoPad in the main() method and then running the program.

1. Modify the main() method in the MemoPadApp driver to accept up to two optional arguments that control the kind of MemoDatabase to be used.

Command-line Execution	Actions taken by MemoPadApp
java MemoPadApp	MemoPadApp uses the default constructor of MemoPad
java MemoPadApp -d	MemoPadApp creates a DefaultMemoDatabase and passes it to the new MemoPad constructor that takes a MemoDatabase parameter
java MemoPadApp -s	MemoPadApp creates an instance of your MyMemoDatabase (use default constructor) and passes it to the new MemoPad constructor
java MemoPadApp -s 100	MemoPadApp creates an instance of your MyMemoDatabase using the new constructor that takes an int parameter, and then passes it to the new MemoPad constructor

If the user gives any other command-line argument, print an error message and return without creating any objects. For example:

          $ java MemoPadApp -oops
          Usage: java MemoPadApp
                 java MemoPadApp -d
                 java MemoPadApp -s [size]
          

Do not modify any other class. Do not modify MemoPad in any other way. We will test your two classes with the original versions of all the other files.

Deliverables

By the due date and time, submit the files

• MyMemoDatabase.java
• MemoPad.java
• MemoPadApp.java