LAB EXERCISE-12 Solution

The objective of this lab is to exercise using built in Java interfaces related to lists and collections.







OVERVIEW:




Write the class ListUtils. The class will contain three static methods, each used for converting between types of collections and related structures.
Download and use a tester module to ensure that your program is correct.



Prepare the assignment for submission and submit it.



This is a lab exercise on which collaboration (including discussing the solution on Piazza or searching online sources) is explicitly permitted.




It is still in your interest to understand and prepare your final submission yourself.




BACKGROUND:




Java contains several different types of interfaces used to organize collections of items. You may already be familiar with the List interface, which is implemented by classes such as the ArrayList. A List represents a collection of elements from which elements can be stored or retreived, in which elements are ordered and can be retrieved by index. A List extends from a Collection, which represents a collection of elements but which may or may not have an order or element index. A Set or Queue is an example of a Collection which is not necessarily a List. Going further, a Collection is an Iterable, a structure which represents a sequence of elements. An Iterable may have persistent elements (such as with a Collection) or it may not (such as a data stream).




In this lab, we will write some utility methods within a class called ListUtils. These three methods will all be static methods, and their purpose will be to perform conversions between objects implementing one type of interface and objects implementing another type. For example, we will write a method for converting from an Iterable object to a Collection, and so on. We will discuss more about how this will work below.




Tip: you will definitely want to import java.util for this lab, since List and all of its relatives use it.




ITERABLE TO COLLECTION TASK:




public static <E Collection<E iterToCollection(Iterable<? extends E iterable)




(3pts) Every Collection is an Iterable but not every Iterable is a Collection. However, if we have an Iterable, it implies a sequence of elements, so we can use that to built a Collection. That is what we will do in this method. To implement the method, we will need to create some kind of Collection object, and add elements from the Iterable's sequence to it one by one.




Hint: we don't want to store the result in a Collection itself, because it is just an interface, but there may be a more familiar choice of structure which implements Collection.




COLLECTION TO LIST TASK:




public static <E List<E collToList(Collection<? extends E coll)




(3pts) As above, every List is a Collection but not every Collection is a List. However, if we have a Collection, it implies a fixed number of elements which can be retrieved in sequence, so we can use that to built a List by numbering the element indices in the order they are retrieved. That is what we will do in this method. To implement the method, we will need to create some kind of List object, and add elements from the Collection.




LIST TO MAP TASK:




public static <E Map<Integer, E listToMap(List<? extends E list)




(3pts) A Map, sometimes known as an associative array or dictionary, is in some ways similar to a List, except that instead of accessing elements by the indices 0, 1, 2, etc., the elements are accessed by a key, which may or may not be in order, and which may or may not be a number. Every element in a Map is stored as a key-value pair (the value of the element plus the key which is used to access it). Thus, when we call the get() method, instead of passing in an int index, we pass in the key corresponding to the element we're looking for. An example of a class which implements the Map interface in Java is the HashMap class.




A List is not a Map and a Map is not a List. However a Map stores collections of data indexed by some kind of mapping. A Map is essentially a dictionary which allows us to look up elements in a collection of data using some reference key to find each element. The reference key for a Map can be any data type, but if we make that data type an Integer, then we can use the key to represent a List index. Thus, in this method, we will take a List and use it to build a Map by using the list index of each element as the element's key within the Map. Thus, if our




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4/15/2019 Lab Exercise-12 for CS 211 / Spring 2019




List contains the elements 2, 4, and 6, then this method will produce a Map with the mappings 0 ⇒ 2, 1 ⇒ 4, and 2 ⇒ 6. As above, this would involve creating an appropriate type of Map and adding the elements from the List.




TESTING:




Download the following:




https://mason.gmu.edu/~iavramo2/classes/cs211/junit-cs211.jar (if necessary)







https://mason.gmu.edu/~iavramo2/classes/cs211/s19/E12tester.java







This is a unit tester which is what we will use to test to see if your classes are working correctly.




When you think your classes are ready (you can try them even without the tester), do the following from the command prompt to run the tests.




On Windows:







javac -cp .;junit-cs211.jar *.java




java -cp .;junit-cs211.jar E12tester




On Mac or Linux:







javac -cp .:junit-cs211.jar *.java




java -cp .:junit-cs211.jar E12tester




In Dr Java:




open the files, including E12tester.java, and click the Test button.







SUBMISSION:




Submission instructions are as follows.




Let xxx be your lab section number and let yyyyyyyy be your GMU userid. Create the directory xxx_yyyyyyyy_E12/



Place the .java file that you've created into the directory.



Create the file ID.txt in the format shown below, containing your name, userid, G#, lecture section and lab section, and add it to the directory.



Full Name: Donald Knuth




userID: dknuth




G#: 00123456




Lecture section: 004




Lab section: 213




compress the folder and its contents into a .zip file, and upload the file to Blackboard.














































































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