Due Thursday, September 30 at 11:59 PM
By the time you have completed this work, you should be able to:
Download everything from the links above into a single directory.
For this assignment, you'll be working with an immutable linked list implementation, a type of persistent data structure. While you (hopefully!) are familiar with linked lists, this implementation is likely very different from the one you're used to. Notably:
append) instead return a new list, reflecting the result of the operation.
For example, [1, 2].append([3, 4, 5]) returns the list [1, 2, 3, 4, 5], leaving the original lists [1, 2] and [3, 4, 5] unmodified.
null to represent the end of a list, we instead use an instance of class Nil.
Cons corresponds to the normal Node class, with the caveat that tail (representing the rest of the list) cannot be null.
Per the prior bullet, if we want to represent a list where tail is empty, then we should have an instance of Nil there.
Cons and Nil are both fully-featured lists in and of themselves.
This is one of the reasons we use Nil instead of null, as we can meaningfully call methods on Nil (unlike null).
Cons and Nil both implement the ImmutableList interface.
If something wants to take a list as a parameter, it should take an ImmutableList; which could be either an empty list (Nil) or a non-empty list (Cons).
In addition to the above bullets, there is a provided JUnit 4 test suite in ImmutableListTest.java.
You will need to compile and run the code. If the code fails to compile, do not try to run it; it either won't work, or you'll run an old, previously-compiled version. The two commands below compile and run the code, respectively. The two commands are slightly different, depending on what system you're running with. If you're on a UNIX-based system (e.g., Mac OS X, Linux), use:
javac -cp .:hamcrest-2.2.jar:junit-4.13.jar -Xlint:all ImmutableList.java Cons.java Nil.java ImmutableListTest.java java -cp .:hamcrest-2.2.jar:junit-4.13.jar org.junit.runner.JUnitCore ImmutableListTest
If you're on Windows command prompt, use these two commands, which use semicolons instead of colons:
javac -cp .;hamcrest-2.2.jar;junit-4.13.jar -Xlint:all ImmutableList.java Cons.java Nil.java ImmutableListTest.java java -cp .;hamcrest-2.2.jar;junit-4.13.jar org.junit.runner.JUnitCore ImmutableListTest
If you're on Windows Powershell, use these two commands, which put some arguments in single quotes:
javac -cp '.;hamcrest-2.2.jar;junit-4.13.jar' -Xlint:all ImmutableList.java Cons.java Nil.java ImmutableListTest.java java -cp '.;hamcrest-2.2.jar;junit-4.13.jar' org.junit.runner.JUnitCore ImmutableListTest
If all tests are passing, you'll see output like the following:
JUnit version 4.13 .................................... Time: 0.053 OK (36 tests)
If tests are failing, the output will instead show which tests are failing.
From there, you can look to see what those tests are doing in the test suite (ImmutableList.java), which will inform you of what needs to be modified.
Note that the provided code will not compile as provided. It's missing the implementations of multiple methods which are needed to make the tests compile.
Add code to Cons.java and Nil.java to get it to compile and pass the tests.
Specifically, you need to implement the following methods for each:
length: returns the length of a list.
As a hint, empty lists (Nil) have length 0.
sum: returns the sum of all the elements of the list.
For our purposes, empty lists (Nil) have a sum of 0.
append: appends two lists together, returning a new list.
contains: returns true if the given list contains the given element, else false.
Example calls to these methods are in ImmutableList.java.
For full credit, your code:
Cons.java and Nil.java; I'll only look at these two files when grading, so any other modifications will be ignored.
for, foreach, while, or do-while).
Any code I provided that uses loops is ok, and should not be modified.
if, switch, or ternary ((...) ? ... : ...)).
Any code I provided that uses loops is ok, and should not be modified.
These restrictions will force you to use recursion for a correct solution, and will also force you to fully exploit virtual dispatch (also known as dynamic dispatch, polymorphism, and ad-hoc polymorphism). While these restrictions will likely be annoying, it will force you to use a key object-oriented feature (virtual dispatch), as well as serve as good practice for later in the course (recursion).
if (list is empty) {
do empty thing
} else {
do non-empty thing
}
...you must instead use virtual dispatch.
For this example, do empty thing would go into the corresponding method definition in Nil, and do non-empty thing would go into the corresponding method definition in Cons.
Cons and Nil, so you really have to implement 8 methods.
That said, the body of each of these methods need only be a single line of code.
If you need much more than a single line for any method, you are likely making this more difficult than it needs to be.
If you're stuck, talk to me.
contains, you do not need to use if, though you'll need to use the short-circuiting nature of ||.
Specifically you can implement this using something like the following:
return head == value || <<recursive call>>;
Log into Canvas, and go to the COMP 333 class. Click “Assignments” on the left pane, then click “Assignment 1”. From here, you need to upload the following files:
Cons.javaNil.java
In addition, if you collaborated with anyone else, be sure to download collaborators.txt and write the names of the people you collaborated with in the file, one per line.
Please submit this file along with the other files.
You can turn in the assignment multiple times, but only the last version you submitted will be graded.