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MP1: Transformations

Strings are an important data type in every programming language. And computers are frequently used to transform and analyze data—including string data. While computers understand bits, bytes, and numbers, humans communicate using letters, words, and sentences.

MP1 comprises two string-based tasks that involve straightforward transformation and modification tasks. They will introduce you to strings, string representation, and simple state machines while also providing more practice with loops and algorithms.

MP1 is due Friday 2/2/2018 @ 5PM. To receive full credit, you must submit by this deadline. In addition, 10% of your grade on MP1 is for submitting code that earns at least 20 points by Tuesday 1/30/2018 @ 5PM. As usual, late submissions will be subject to the MP late submission policy.

1. Learning Objectives

The purpose of MP1 is to familiarize you with Java strings and string processing. You’ll begin to learn how to:

interpret text as a series of lines, lines as a series of words, words as a series of characters, and characters themselves as numbers
use simple looping constructs to iterate over arrays of strings and strings themselves
implement a simple state machine
correct Javadoc comments

We’ll also continue to reinforce the learning objectives from MP0.

2. Assignment Structure

MP1 consists of two short programs:

PrintLines.java: parses a script and returns lines for a particular actress (or actor)
Encrypt.java: encrypts and decrypts text using the so-called Caesar Cipher

You may find our official MP1 online documentation helpful in understanding what each function is supposed to do.

2.1. Obtaining MP1

Use this GitHub Classroom invitation link to fork your copy of MP1. Once your repository has been created, import it into IntelliJ following our assignment Git workflow guide.

2.2. Your Goal

All programs and incomplete and need work. The structure of each program is similar:

Each contains a main method that solicits input from the user. You do not need to modify the main methods, but you should understand how they work.
User inputs are passed to a separate helper function that you are assigned to write. These functions do the heavy lifting for each program: returning an actress’s lines (printLinesFor), and encrypting (encrypt) and decrypting (decrypt) text.
Each program includes a test suite: PrintLinesTest.java and EncryptTest.java. The test suite does not test the main method. Instead, it directly tests the method that you are assigned to write.

Your goal is to correctly implement the missing methods so that all of the tests pass. Doing so will earn you almost full credit on the assignment—but see the section on style below.

3. How to Approach MP1

All of the MP0 guidelines still apply. In addition, let us provide some new advice for MP1.

3.1. Review `java.lang.String`

An important part of MP1 is understanding the various methods that you can call on Java strings. The best place to find a complete list is the Javadoc documentation for the Java String type.

You will definitely want to review the list of String methods to find things that might be useful. Specifically, the String methods split, toLowerCase, toUpperCase, startsWith may be useful in completing MP1—particularly for printLinesFor.

3.2. Documenting Your Work

While comments are not processed by the computer, they are some of the most important things that you will write (and read) as a software developer.

The reason that comments are so important is simple—while the code you write is run by a computer, is is used by other human beings. Regardless of whether a computer can understand what your code is trying to do, if other people cannot you will be in trouble. In the open-source community, nobody will be able to use your contributions—even if they want to. At a job, poorly documented code will get you fired extremely quickly.

So an important job when writing code is documenting it so that others can use it. We will give you practice at doing this on the MPs, and also go over it several times during lab sections. But here are some general guidelines to get you started:

3.2.1. Documentation for packages and functions is extremely important

This is one of the reasons that we are forcing you to write Javadoc comments, since they can be easily used to generate documentation. Here is an example from this week’s lab. Well-written documentation makes it possible for others to use your code without understanding your implementation. That is critical to modern software development.

3.2.2. Comments within functions should be used sparingly

On the other hand, comments within your code should be used sparingly. They are not a substitute for writing clear and readable code.

A good way to think about comments in your code is as a chance to explain something unusual that might confuse another person that is reading your code—or, more likely, you!

3.3. Writing Readable Code

Comments and documentation are not a substitute for writing reading code. Think of it this way—documentation is for others that will try to use your code, including collaborators and co-workers. Comments document unusual situations, but are primarily for you, not for others, since you’re the one who’s most likely to have to read (and probably debug) your code.

Readable code is even more important for you and you alone. So treat writing code that is clear and easy to understand as personal and selfish challenge, since it is most likely to benefit you.

3.3.1. Good variable names

One basic aspect of writing good code is good choices of variable names. A good variable name should allow me to understand how it is being used without reading much of the code.

Good variable names depend a lot on context, but one good practice to get in to is to avoid generic names like i, j, index, count, etc. Try more specific names like indexInString, countOfLetters, etc. count could be anything—whereas countOfLetters lets me know more about what is being counted. Keystrokes are cheap, understanding is expensive.

3.4. Getting Help

The course staff is ready and willing to help you every step of the way! Please come to office hours, or post on the forum when you need help. You should also feel free to help each other, as long as you do not violate the academic integrity requirements.

4. Grading

MP1 is worth 100 points total, broken down as follows:

40 points: PrintLines.java
- 10 points for submitting code that compiles
- 30 points for passing the test
40 points: Encrypt.java
- 10 points for submitting code that compiles
- 30 points for passing the test
10 points for no checkstyle violations
10 points for submitting code that earns at least 20 points before Tuesday 1/30/2018 @ 5PM.

Programming is a skill, and you learn it with regular consistent practice. If you wait until the day of the deadline, it’s unlikely that you’ll get as much practice and learn as much as if you start early. When you give yourself enough time to complete the MP, you can also slow down, enjoy yourself, and do things right. Take a few extra minutes to learn more about a library that you’re using, or clean up your code so that it really shines. The earlier you start, the more likely you’ll do some of these useful things.

So, we’re going to incentive you starting on time. 10% of MP2 is earned by submitting something that earns 20 points by Tuesday 1/30/2018 @ 5PM. You don’t have to do much to get 20 points, but we hope that it will get you reading and think about the MP before the end of the week, when office hours are packed.

4.1. Test Cases

Like MP0, we have provided exhaustive test cases for each part of MP1. Please review the MP0 testing instructions.

4.2. Autograding

Like MP0, we have provided you with an autograding script that you can use to estimate your current grade as often as you want. Please review the MP0 autograding instructions.

4.3. Style Points

Review the style notes from MP0. For MP1 you will have to correct some existing style errors. Please look at the Javadoc comments on other provided functions for examples of how to use the @param and @return tag.

5. Submitting Your Work

Follow the instructions from the submitting portion of the CS 125 workflow instructions.

6. Cheating

Please review the CS 125 cheating policies.

All submitted MP source code will be checked by automated plagiarism detection software. Cheaters will receive stiff penalties—the hard-working students in the class that are willing to struggle for their grade demand it.