Preamble. Singly linked lists. Collaboration policy and academic integrity. Getting help

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1 CS2110 Spring 2016 Assignment A. Linke Lists Due on the CMS by: See the CMS 1 Preamble Linke Lists This assignment begins our iscussions of structures. In this assignment, you will implement a structure calle a oubly linke list. Rea the whole hanout before starting. Near the en, we give important instructions on testing. At the en of this hanout, we tell you what an how to submit. We will ask you for the time spent in oing A, so please keep track of the time you spen on it. We will report the minimum, average, an maximum. Learning objectives Learn about an master the complexities of oubly linke lists. Learn a little about inner classes. Learn an practice a soun methoology in writing an ebugging a small but intricate program. Collaboration policy an acaemic integrity You may o this assignment with one other person. Both members of the group shoul get on the CMS an o what is require to form a group well before the assignment ue ate. Both must o something to form the group: one proposes, the other accepts. People in a group must work together. It is against the rules for one person to o some programming on this assignment without the other person sitting nearby an helping. Take turns riving using the keyboar an mouse. With the exception of your CMS-registere group partner, you may not look at anyone else's coe, in any form, or show your coe to anyone else (except the course staff), in any form. You may not show or give your coe to another stuent in the class. Getting help If you on't know where to start, if you on't unerstan testing, if you are lost, etc., please SEE SOMEONE IMMEDIATELY an instructor, a TA, a consultant. Do not wait. If you fin yourself spening more than an hour or two on one issue, not making any progress, STOP an get help. Some ponering an thinking with no progress is helpful, but too much of it just wastes your time. A little in-person help can o woners. See the course webpage for contact information. Singly linke lists The iagram below represents the list of values [6, 7, ]. The leftmost object,, is calle the er. It contains two values: the of the list,, an a pointer to the first noe of the list. Each of the other three objects, of class M, contains a value of the list an a pointer to the essor noe of the list or if there are no more noes in the list. This structure is call a singly linke list, or just linke list. For simplicity in iscussions, for any list, we may use the notation [0] for its first element, [1] for its secon, an so on. Below, [0] = 6. But remember, this is not Java notation for lists. 6 7

2 CS2110 Spring 2016 Assignment A. Linke Lists Due on the CMS by: See the CMS 2 Many structures can be use to implement a list, Different programs use lists in ifferent ways. One chooses a structure that optimizes a program in some way, making the most frequently use operations as fast as possible. For example, maintaining a list in an array b has the avantage that any element, say number i, can be reference in constant time, using (typically) b[i]. But maintaining a list in an array has isavantages: (1) The of the array has to be etermine when the array is first create, (2) One nees a variable that contains the number of values in the list, an () Inserting or removing values at the beginning takes time proportional to the of the list. A singly linke list has these avantages: (1) The list can be any, an (2) Inserting (or removing) a value at the beginning can be one in constant time. It takes just a few operations, boune above by some constant: Create a new object an change a few pointers. On the other han, to reference element i of the list takes time proportional to i one has to sequence through all the noes 0..i-1 to fin it. Exercise At this point, you will gain more unerstaning by oing the following, to construct a linke list that represents the sequence [4, 6, 7, ]. Do what follows, on t just rea it. (1) Copy the linke list iagram shown near the bottom of the previous page. (2) Below that iagram, raw a new object of class M, with 4 in fiel an in fiel. () Now change fiel of the new noe to point to noe an change fiel to point to the new noe. (4) Finally, change fiel. to 4. The iagram now represents the list [4, 6, 7, ]. Doubly linke lists A singly linke list has fiel in the er an fiel in each noe, as shown above. A oubly linke list has, in aition, a fiel tail in the er an a fiel in each noe, as shown below. In the iagram below, one can traverse the list of values in reverse: first.tail., then.tail.., then.tail... This oubly linke lists represents the same sequence [6, 7, ] as the singly linke list given above but the structure lets us easily enumerate the values in reverse, [, 7, 6], as well as forwar. The major avantage of a oubly linke list over a singly linke list is that, given a noe n (containing something like ), one can get to n s ecessor an essor in constant time. For example, removing noe n from the list can be one in constant time, but in a singly linke list, the time may epen on the length of the list (why?). In A, you will implement a oubly linke list using the representation below. The er will be of class DLinkeList (abbreviate LL below), an noes will be objects of class Noe (given by M below), Stuy this iagram carefully. All further work rests on unerstaning this structure. 6 7 tail We often write such linke lists without the tabs on the objects an even without names in the pointer fiels, as shown below. No useable information is lost, since the arrows take the place of the object pointer-names. 6 7 tail

3 CS2110 Spring 2016 Assignment A. Linke Lists Due on the CMS by: See the CMS A oubly linke list allows the following operations to be execute in constant time using just a few assignments an perhaps if-statements to appen a value to the list, prepen a value (insert an element at the beginning of the list), insert a value before or after a given element, an elete a value. It will be your job to implement these operations in constant time. In an array implementation of such a list, most of these operations coul take time proportional to the length of the list in the worst case. This assignment We give you a skeleton for class DLinkeList<E> (where E is any class-type). It extens class java. util.abstractlist<e>. The release coe contains many methos, some alreay written. The ones you have to write are annotate with a //TODO comment, an they inicate the orer in which the methos must be written. Please on t elete these comments. The class also contains a efinition of Noe (it is an inner class; see below). You must also evelop a JUnit test class, DLinkeListTest, that thoroughly tests the methos you write. We give important irections on writing an testing/ebugging below. Generics The efinition of DLinkeList has DLinkeList<E> in its er. Here, E is a type parameter. To eclare a variable v that can contain (a pointer to) a linke list whose elements are of type Integer, use: DLinkeList<Integer> v; // (replace Integer by any class-type you wish) Similarly, create an object whose list-values will be of type String using the new-expression: new DLinkeList<String>() We will introuce you to generic types more thoroughly later in the course. Access moifiers an testing Java has four ifferent access moifiers: public, private, protecte, an package (you can t place package in your program; it s what you get if you on t put an access moifier). This table shows you what each means: moifier class package subclass worl public Y Y Y Y protecte Y Y Y N package Y Y N N private Y N N N Some of the methos in DLinkeList are public because we want users to be able to use them. But other methos are helper methos, which shoul remain unknown an inaccessible to users. So, we coul make them private. But that makes it very har to test the helper methos in a JUnit testing class! How can we call a metho in orer to test it if we can t access it? Instea, we give the helper methos access moifier package (meaning they have no explicit access moifier). Then, since the JUnit testing class an DLinkeList are in the same package, the efault package, the JUnit testing class can reference the helper methos. When writing a realistic class that you want others to use, you woul put the class in a real package, not the efault package, along with your testing class. When one, you coul create a jar file (we ll see that later) containing your class (still in a package), an the user woul use this. The user woul not be able to put a class in the same package, so the user woul not be able to get at the helper methos. Isn t that neat?

4 CS2110 Spring 2016 Assignment A. Linke Lists Due on the CMS by: See the CMS 4 Inner classes Just as one can eclare a variable (fiel) an a metho in a class, one can eclare another class. Class Noe is eclare within class DLinkeList. It is calle an inner class. We ll talk more about inner classes later. The methos of DLinkeList can an shoul reference the fiels of the inner class irectly. There is no nee for getter an setter methos for these fiels. In the JUnit testing class, you will nee to eclare local variables of class Noe. Here is an example of how to o it, where b is a variable of type DLinkeList<Integer>. DLinkeList<Integer>.Noe noe= b.gethea(); What to o for this assignment 1. Start a project a (or another name) in Eclipse, ownloa file DLinkeList.java from the course website or the Piazza, an put the file files into a, in the efault package. Create a new JUnit testing class. Name it DLinkeListTest, which is what Eclipse will try to name it. Inner class Noe is complete; you o not have to an shoul not change it. Write the 1 methos inicate in class DLinkeList, testing each thoroughly as suggeste below. Some of the methos are helper methos, which is where the core functionality shoul be. The rest are public methos, which shoul be mae rather small by using the helper methos. We provie extensive comments to help you out. On the first line of file DLinkeList.java, replace nnnn by your netis an hh an mm by the hours an minutes you spent on this assignment. If you are oing the project alone, replace only the first nnnn. Please o all this carefully. If the minutes is 0, replace mm by 0. We wrote a program to extract these times, an when you on t actually replace hh an mm but instea write in free form, that causes us trouble. Also, please take a few minutes to tell us what you thought of this assignment. 2. Submit the assignment (both classes) on the CMS before the en of the ay on the ue ate. Graing: 65 points will be base on functional correctness an 5 points on efficiency of function getnoe, as specifie in the comments within getnoe. 0 points will be base on testing: we will look carefully at class DLinkeListTest. So, overall, if you on t test a metho properly, points might be eucte in three places: (1) the metho might not be correct, (2) the metho might not use the best way to get to a noe, an () the metho might not be teste properly. Further guielines an instructions Some methos that you have to write have an extra comment in the boy, giving more instructions an hints on how to write it. Follow these instructions carefully. Writing a helper metho: Five of the methos are helper methos. You have to be extremely careful to write them correctly. It is best to raw the linke list. If the metho changes the list, raw the list before an after the change, note which variables have to be change, an then write the coe. Not oing this is sure to cause you trouble. Be careful with a metho like appen because a single picture oes not tell the whole story. Here, two cases must be consiere: the list is empty an it is not empty. So two sets of before-an-after iagrams shoul be rawn. This will probably means implementing the metho with two cases using an if-statement. Methoology on testing: Write an test one group of methos at a time! Writing all an then testing will waste your time, for if you have not fully unerstoo what is require, you will make the same mistakes many times. Goo programmers write an test incrementally, gaining more an more confience as each metho is complete an teste.

5 CS2110 Spring 2016 Assignment A. Linke Lists Due on the CMS by: See the CMS 5 Determining what test cases to use: In testing a metho, you must o two things (1) make sure that each statement of the metho is exercise in at least one test case. Thus, if the metho has an if-statement, at least two test cases are require. (2) Ensure that corner cases or extreme cases are teste. In the context of oubly linke lists, an empty list an a list may be extreme cases, epening what is one to the list. When finishe with a metho, to etermine test cases, look carefully at the coe, base on the above points (1) an (2). What to test an how to test it: Determining how to test a metho that changes the linke list can be time consuming an error prone. For example: after inserting 6 before 8 in list [2, 7, 8, 5)], you must be sure that the list is now [2, 7, 6, 8, 5]. What fiels of what objects nee testing? What an fiels? How can you be sure you in t change something that shouln t be change? To remove the nee to think about this issue an to test all fiels automatically, you must must must o the following. In class DLinkeList, FIRST write the constructor, function, an function tostringrev, as best you can. In writing tostringrev, o not use fiel. Instea, use only fiels tail in class DLinkeList an the an fiels of noes. Do not put in JUnit testing proceures for tostringrev, because it will be teste when testing metho appen, just as getters were teste in testing a constructor in A1. For example, after completing the constructor,, an tostringrev, you can test that they work properly on the empty list using this public voi testconstructor() { DLinkeList<Integer> b= new DLinkeList<Integer>(); assertequals("[]", b.tostring()); assertequals("[]", b.tostringrev()); assertequals(0, b.()); } Testing function appen will fully test tostringrev. You are testing those two functions together. Each call on appen will be followe by assertequals calls, similar to those in testconstructor, followe by a test that the returne value is public voi testappen() { DLinkeList<String> ll= new DLinkeList<String>(); DLinkeList<String>.Noe n= ll.appen("ross"); assertequals("[ross]", ll.tostring()); assertequals("[ross]", ll.tostringrev()); assertequals(1, ll.()); assertequals(ll.gettail(), n); } Many of your tests of your functions will have similar assertequals calls. That way, you on t have to think about what fiels to test: you test them all. Once you have implemente, getnoe, an get, the implementation for methos equals inherite from AbstractList will work as well, so you can test using that in aition to using tostring an tostringrev. Woul you have thought of using tostringrev an tostringrev like this? It is useful to spen time thinking not only about writing the coe but also about how to simplify testing.