CSE 373, Winter 2018: Project 1: Part 1

Summary

Due Wed, Jan 10 at 11:30pm

In this half of the assignment, you will implement the data structures you will be using on the second half.

Part 1a: Write missing tests

Task: Modify TestDoubleLinkedList.java and add in tests for the delete method.

In part 1a, you will practice writing some unit tests using jUnit.

Start by skimming through TestDoubleLinkedList.java and familiarize yourself with the tests we have given you. Since this is the first assignment, we've given you most of the tests you need, except for a few. Can you see what tests are missing?

There are no tests for the DoubleLinkedList.delete(...) method! Add new methods testing your delete method.

You may find the following documents from the resources page to be particularly useful:

  1. JUnit tutorial
  2. Tips on testing code

You may be tempted to do this step last and jump straight into writing code. This is a bad habit: that kind of cowboy attitude doesn't really scale to larger projects.

Part 1b: Implement DoubleLinkedList

Task: complete the DoubleLinkedList class.

A doubly-linked list is a similar to the singly-linked lists you studied in CSE 143 except in two crucial ways: your nodes now have pointers to both the previous and next nodes, and your linked list class has now have pointers to both the front and back of your sequence of list node objects.

Visually, the singly linked lists you studied in CSE 143 look like this:

Singly linked list diagram

Doubly-linked lists containing the same data will look like this:

Doubly linked list diagram

Your implementation should:

  1. Be generic (e.g. you use generics to let the users store objects of any types in your list)
  2. Implement the IList interface.
  3. Be as asymptotically efficient as possible.
  4. Contain exactly as many node objects as there are items in the list. (If the user inserts 5 items, you should have 5 nodes in your list).

Warning: correctly implementing a doubly-linked list will require you to pay careful attention to edge cases. Some tips and suggestions:

  • Think carefully about the end cases (front and back) and what should happen when the list is empty or nearly empty.

  • Write pseudocode for your methods before writing code. Avoid immediately thinking in terms of listnode manipulation – instead, come up with a high-level plan and write helper methods that abstract your node manipulations. Then, flesh out how each helper method will work.

    Or to put it another way, figure out how to refactor your code before you start writing it. Your code will be significantly less buggy that way.

What is an iterator?

When implementing DoubleLinkedList, you will also need to implement an iterator for the class.

You should have studied iterators in CSE 143, and we should have (briefly) covered them in lecture, but here is a review of what iterators are in case you need it:

An iterator object is a kind of object that lets the client efficiently iterate over a data structure using a foreach loop.

Whenever we do something like:

for (String item : something) {
    // ...etc...
}

...Java will internally convert that code into the following:

Iterator<String> iter = something.iterator();
while (iter.hasNext()) {
    String item = iter.next();
    // ...etc...
}

When you call iter.next() for the first time, the iterator will return the first item in your list. If you call iter.next() again, it'll return the second item. Once the user calls iter.next() enough time and encounters the last item in the list, calling iter.next() once again should throw an NoSuchElementException.

The iter.hasNext() method will return true if calling iter.next() will safely return a value, and false otherwise.

You can see an example of this expected behavior within your tests.

Notice that the iterator is behaving somewhat similar to a Scanner, except that it's iterating over a data structure instead of a String or file.

In practice, iterators can also be used to safely modify the object they're iterating over. We will not be implementing this functionality in this class: you should assume the client will never modify a data structure while they're iterating over it.

Part 1c: Implement ArrayDictionary

Task: complete the ArrayDictionary class.

Your ArrayDictionary class will internally keep track of its key-value pairs by using an array containing Pair objects.

Dictionary<String, Integer> foo = new ArrayDictionary<>();
foo.put("a", 11);
foo.put("b", 22);
foo.put("c", 33);

Your internal array should look like the following:

ArrayDictionary internal state 1

Now, suppose the user inserted a few more keys:

foo.put("d", 44);
foo.remove("b");
foo.put("a", 55);

Your internal array should now look like the below. Notice that we've updated the old key-value pair for "a" to store the new value. We've also removed the key-value pair for "b".

ArrayDictionary internal state 2

This means you will need to scan through the internal array when retrieving, inserting, or deleting elements. If your array is full and the user inserts a new key, create a new array double the size of the old one and copy over the old elements.

Once completed, the design and logic of your ArrayDictionary should feel very similar to the ArrayIntList objects you previously studied in CSE 143.

This seems inefficient...?

You may have noticed that the implementation we've described above does not feel very efficient – it would take \(\mathcal{O}(n)\) time to lookup a key/value pair.

This is true! We need dictionaries to do interesting things but also have not covered how to implement truly efficient dictionaries yet. We've compromised by having you implement a basic one for now.

You'll implement more efficient dictionaries later this quarter, as a part of your second project.

If you finished early...

If you finished early, you may want to start on the writeup portion of this project (see the project 1, part 2 spec for more details). While the writeup is not due this week, it contains questions that focus exclusively on material from part 1.

You may find working on the writeup to be a good way of helping you determine whether your data structures are designed soundly.

Deliverables

The following deliverables are due on Wed, Jan 10 at 11:30pm.

A single person from your partnership should submit the entire contents of your src folder as a zip file on Canvas.

Please follow the above instructions EXACTLY. Do not remove, rearrange, or rename any files or folders: just zip your src folder. (This means you will be submitting a lot of instructor-provided code along with your files. This is fine.)

Before submitting, be sure to double-check that:

  • You are submitting your completed TestDoubleLinkedList, DoubleLinkedList, and ArrayDictionary classes which all behave as expected.
  • You ran checkstyle and fixed all issues it reported with the files you edited.