Programming Assignment 3

Due Date: Tuesday, January 31, 10:00PM Pacific Time

Learning Goals

Practice writing classes and conditionals
Do some open-ended exploration of Java features

Collaboration

Different assignments in this course have different collaboration policies. On this assignment, you can collaborate with anyone in the course, including sharing code. In your submission, give credit to all students and course staff who helped you with this assignment by noting their name and how you used their ideas or work. Note that using someone’s work without giving credit to them is a violation of academic integrity.

Starter Code

You can download the starter code for this assignment here:

https://github.com/ucsd-cse11-w23/cse11-pa3-starter

Start Early!

Start working on the assigment early. Even an hour a day can be very helpful to make sure you finish before the deadline.

Submission Checklist

You should submit:

Task 1

Drill 1 (autograded)

Write three classes as described below. They do not need to have any methods or constructors. Save them in the file Drill1.java.

A class named A with two fields, int f1 and String f2
A class named B with two fields, A field1 and String field2
A class named C with three fields, B fieldB, A fieldA, int field3

Drill 2 (autograded)

In the file Drill2.java, add the following class definitions (you can copy/paste them from here):

class C1 {
  C2 other;
  C1(C2 other) {
    this.other = other;
  }
}

class C2 {
  int x;
  C2(int x) {
    this.x = x;
  }
}

Then add a class definition called Drill2 with the following fields:

A field named first of type C2 with its x field equal to 10
A field named second of type C1. It’s value should be a reference to a C1 object with its other field set to any C2 object other than the one stored in first (you can create another C2 object for this).
A field named third of type C1. It’s value should be a reference to a C1 object with its other field the same C2 object as the one stored in the first field.

Drill 3 (autograded)

In the file Drill3.java, write a class called TextTweet that has two fields: one field called contents of type String, and one field called likes of type int. Give it a constructor of two arguments that initializes those fields. In it, write the following methods:

hasMention which takes a String called username and checks if the string @ followed by that username apppears in the Tweet contents, returning true if it does and false otherwise. (There are some interesting cases for this method. For example, to check if we have the username “dummy” in “@dummy1 @dummy2”, hasMention() should return false in this case because username dummy1 and dummy2 is not the same as dummy, while “hello @dummy world” and “CSE 11 is a cool class @dummy” should return true)
hasLike which takes no arguments and returns true if the tweet has one or more likes, false otherwise.
firstMention which takes no arguments and returns a String containing the substring between the first appearance of the @ character in the contents and the first space character after that. Do not include the @ character and the space character. If there is no space after the @, or if there’s no @, the empty string "" should be returned.

(You may find some String methods in the Java documentation useful)

Also in Drill3.java, write a class called ReplyTweet that has three fields: one called replyTo of type TextTweet, one called contents of type String, and one called likes of type int. Give it a constructor of three arguments that initializes these fields. In it, write the following methods:

morePopularReply which takes no arguments and returns true if this ReplyTweet has more likes than the TextTweet it is replying to
allLikes which takes no arguments and returns the sum of the likes on this ReplyTweet and on the TextTweet it is replying to
hasMention which takes a String called username and checks if the string @ followed by that username apppears in this ReplyTweet’s contents or in the TextTweet that is being replied to.

We highly recommend adding a class to this file called Drill3 that has any tests or examples you used to help verify that your methods worked as you expected.

Drill 4 (autograded)

In a file called Drill4.java, write a class Drill4 with the following methods (you may find some Math methods in the Java documentation useful):

phaseOfWater which takes an int and returns "vapor" if the number is greater than or equal to 100, "liquid" if the number is less than 100 and greater than 0, and "solid" if the number is less than or equal to 0.
maxDifference which takes three ints and returns the largest absolute difference between any two of them. For example, maxDifference applied to 1, -1, and 5 should return 6 because the difference between -1 and 5 is 6 which is greater than 2 or 4 (the differences between -1 and 1, and between 1 and 5).
ringArea which takes two doubles representing the radius of an inner circle and an outer circle, and returns the area of the ring between them as a double. Assume both inputs are positive and that the first number is smaller than the second. Recall that the area of a circle is πr². You can use Math.PI, a field conveniently defined for us by Java, as a constant for the value of π.

In addition, you must write at least three interesting tests for each method above, and include the expected values. You can test them in the same way as we did in class and previous two PAs. You can use the tester package if you want, but we’re not grading for it. In PA4 we will explicitly require it in some cases to make sure everyone gets practice with it.

Task 2

Open-Ended 1 (manually graded)

Consider the following statements about Java programs:

Statement A: In Java, two different classes can define a field with the same name and type.
Statement B: In Java, one class can define two fields with the same name as long as they have different types.
Statement C: In Java, two different methods in the same class can have the same parameter name, and arguments passed to one of those methods don’t affect the parameter in the other.

For each statement, write a small Java program that demonstrates whether it is true or false. In the programs you should define some classes that reflect the statements. You can choose whatever names you want for the classes. Put the class definitions in the files Open1A.java, Open1B.java, and Open1C.java. Inside the files, you should also include an Open1A/Open1B/Open1C class with some instances of the classes you just create.

To show that a statement is true, write a Java program that matches the statement, doesn’t produce an error when run, and produces some meaningful output when ./run.

To show that a statement is false, write a Java program that matches the statement and produces an error when run, demonstrating that Java programs cannot do what the property says.

Include both the program and the output of running the program as your submission; you can upload screenshots as images clearly named with Open1A, Open1B, etc in the title, or copy-paste the text output into a comment in your code.

Open-Ended 2 (manually graded)

Create a class named R that has a field of type String and a field of type R. Give it a constructor that initializes both fields. Put the class in a file called ExamplesR.java. Add an ExamplesR class to this file, and answer the following questions in that file:

Construct an example R object. Were you able to? Explain your example if you were able to, and explain why you think it’s not possible if you weren’t.
On Twitter, it’s possible to reply to a reply to a Tweet (that’s not a typo, it’s a reply to a reply). This is true of many systems, like email, Facebook comments, Piazza followups, and so on. With the class structure in Drill3 with ReplyTweet and TextTweet (that is, without changing the fields as described above), could you construct an example of a reply to a reply to a Tweet? Why or why not?

Submission

You will submit all of your files to the pa3 assignment on Gradescope:

On the Gradescope upload screen, you can keep clicking “Browse Files” to select more than one file for your upload; you can select them one at a time or use your operating system’s multi-select (Shift-Click usually works) to select them all and drag them onto the upload area, or other options that you find that work.
You can also make a zip archive of all of your files and upload them all at once if you prefer.

The parts marked autograded will be graded automatically in Gradescope based on tests we wrote. The parts marked manually graded will be graded by the course staff after the due date.