cs1302-ce18 Generic Method Implementation

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-- Age Old Saying

This class exercise explores functional interfaces, lambda expressions, and method references in conjunction with generic methods and interfaces. In this exercise, only the generic method signatures will be provided. Implementation details are left to the student.

Course-Specific Learning Outcomes

• LO2.d: (Partial) Implement new generic methods, interfaces, and classes in a software solution.
• LO2.e: (Partial) Utilize existing generic methods, interfaces, and classes in a software solution.
• LO4.a: (Partial) Design, create and use interfaces in a software solution.
• LO4.b: (Partial) Utilize interface-based polymorphism in a software solution.

Prerequisites

• The Java™ Tutorials: Generic Methods
• The Java™ Tutorials: Lambda Expression
• The Java™ Tutorials: Method References

References

• java.util.function.Predicate Interface Documentation
• java.util.function.Function Interface Documentation
• java.util.function.IntFunction Interface Documentation

Questions

In your notes, clearly answer the following questions. These instructions assume that you are logged into the Odin server.

NOTE: If a step requires you to enter in a command, please provide in your notes the full command that you typed to make the related action happen. If context is necessary (e.g., the command depends on your present working directory), then please note that context as well.

Getting Started

1. Use Git to clone the repository for this exercise onto Odin into a subdirectory called cs1302-ce18:

   $ git clone --depth 1 https://github.com/cs1302uga/cs1302-ce18.git
   

2. Change into the cs1302-ce18 directory that was just created and look around. There should be multiple Java files contained within the directory structure. To see a listing of all of the files under the src subdirectory, use the find command as follows:

   $ find src
   

Exercise Steps

Checkpoint 1 Steps

1. Take a close look at the printlnMappedMatches method and its associated Javadoc in MoreLambdaFun.java. The exact signature for this method is:

   private static <T> void printlnMappedMatches(T[] t, Predicate<T> p, Function<T, String> f)

   Implement the printlnMappedMatches method in MoreLambdaFun.java. You do not need to use a lambda for this step. You will only need to use the Function<T, R> and Predicate<T> references to call the appropriate methods.

2. At the end of the main method of MoreLambdaFun class:

   1. Declare a variable bonusPred of type Predicate<Quiz> and assign to it, using a lambda expression, a reference to an object that tests if the quiz is a bonus quiz. Remember, you can always refer to the API documentation for the associated interface when trying to determine the layout of your lambda.

   2. Declare a variable numberFunc of type Function<Quiz, String> and assign to it, using a lambda expression, a reference to an object that takes a Quiz object as a parameter and returns a String containing the quiz number and at least one other piece of information about the quiz (other than bonus). Remember, you can always refer to the API documentation for the associated interface when trying to determine the layout of your lambda.

3. Call the printlnMappedMatches using your newly created variables. Make sure to provide sufficient output so that it will be easy to convince your TA or instructor that everything is working properly.

4. Compile your code and run it. Then, stage and commit all changes.

5. Using lambdas, write the code to print quiz numbers for all quizes that have a time limit that is under twenty minutes. Make sure to provide sufficient output so that it will be easy to convince your TA or instructor that everything is working properly.

6. Make sure your code passes the checkstyle audit then stage and commit all changes.

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Checkpoint 2 Steps

1. Take a close look at the copyOf method and its associated Javadoc in MoreLambdaFun.java. The exact signature for this method is:

   public static <T> T[] copyOf(T[] a, int l, IntFunction<T[]> g)

   Answer the following questions about this method in your notes:

   1. What is the generic type parameter?

   2. Specifically, what reference types can replace T?

   3. In order to call this method, we need a reference to an object of a class that implements IntFunction<T[]>. The interface is defined as IntFunction<R>. Here, we replace R with T[]. Keep this in mind when inspecting the API documentation for IntFunction<R>.

   Hint: See the toArray documentation from the GenList project, which also takes an IntFunction parameter.

   1. Write the full, expanded method signature (with the replaced types) of the single, abstract method of IntFunction<T[]> in your notes. Pay careful attention to the return type and the type of the formal parameter.

2. After carefully reading its Javadoc comment, implement the copyOf method in MoreLambdaFun.java. You do not need to use a lambda for this step.

3. Stage and commit all changes.

4. At the end of the main method of the MoreLambdaFun class:

   1. Declare a variable lessQuizzes of type Quiz[] and, using your copyOf method, assign to it a copy of the array referred to by quizzes containing half as many quizzes (containing the first half of the quizzes). You should supply the g parameter using a regular lambda expression.

      Hint: See the toArray documentation from the GenList project, which also takes an IntFunction parameter.

   2. Using a for-each loop, print the quiz numbers of all Quiz references in lessQuizzes.

   3. Declare a variable moreQuizzes of type Quiz[] and, using your copyOf method, assign to it a copy of the array referred to by quizzes containing four (4) more spots for quizzes (all null). You should supply the g parameter using an array constructor method reference.

   4. Using an appropriate loop, print the quiz numbers of all non-null Quiz references in moreQuizzes. Also, print the length of the array to make sure it is the proper size.

5. Make sure your code passes the checkstyle audit then stage and commit all changes.

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Checkpoint 3 Steps

1. Create and document a static method called makeQuizArray that, if written correctly, a method reference for that method can be used to supply the g parameter in a call to your copyOf method. Then, at the end of the main method of the MoreLambdaFun class:

   1. Declare a variable twentyQuizzes of type Quiz[] and, using your copyOf, assign to it a copy of the array referred to by quizzes containing twenty spots for quizzes (with trailing null values as described in the Javadoc for copyOf). You should supply the g parameter using a method reference to the method you created in the previous step.
   2. Using an appropriate loop, print the quiz numbers of all non-null Quiz references in twentyQuizzes. Also, print the length of the array to make sure it is the proper size.

2. Make sure your code passes the checkstyle audit then stage and commit all changes.

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Submission Steps

Each student needs to individually submit their own work.

1. Create a plain text file called SUBMISSION.md directly inside the cs1302-ce18 directory with the following information.

   1. Your name and UGA ID number;
   2. Collaborator names, if any; and
   3. If you created the API website, include the full link to the site you generated.

   Here is an example of the contents of SUBMISSION.md.

   1. Sally Smith (811-000-999)
   2. Collaborators: Joe Allen, Stacie Mack
   3. https://webwork.cs.uga.edu/~user/cs1302-ce18-doc
   

2. Change directories to the parent of cs1302-ce18 (e.g., cd .. from cs1302-ce18). If you would like to make a backup tar file, the instructions are in the submissions steps for ce02. We won't repeat those steps here and you can view them as optional.

3. Use the submit command to submit this exercise to csci-1302:

   $ submit cs1302-ce18 csci-1302
   

   Read the output of the submit command very carefully. If there is an error while submitting, then it will displayed in that output. Additionally, if successful, the submit command creates a new receipt file in the directory you submitted. The receipt file begins with rec and contains a detailed list of all files that were successfully submitted. Look through the contents of the rec file and always remember to keep that file in case there is an issue with your submission.

   Note: You must be on Odin to submit.

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Copyright © Michael E. Cotterell, Bradley J. Barnes, and the University of Georgia. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License to students and the public and licensed under a Creative Commons Attribution-NonCommercial 4.0 International License to instructors at institutions of higher education. The content and opinions expressed on this Web page do not necessarily reflect the views of nor are they endorsed by the University of Georgia or the University System of Georgia.