Project 1: Data Structures

Introduction
Getting the Skeleton Files
- Packages
The Deque API
Project Tasks
- 1. Linked List Deque
- 2. Array Deque
Extra Credit: Checkpoint
Testing
Extra Credit: Autograder
MaxArrayDeque
Deque Interface
Guitar Hero
- The GH2 Package
GuitarString
- GuitarHeroLite
Just For Fun: TTFAF
Even More Fun
Why It Works
Submission and Grading
Frequently Asked Questions
- Deque
  - Q: How should I print the items in my deque when I don’t know their type?
  - Q: I can’t get Java to create an array of generic objects!
  - Q: I tried that but I’m getting a compiler warning?
  - Q: How do I make my arrows point to particular fields of a data structure?
- Guitar Hero
  - I’m getting a “class file contains wrong class” error.
  - I’m getting a message that I did not override an abstract method, but I am!
  - When I try to run the provided tests I get “No runnable methods”.
  - When I try to compile my code, it says type K#1 is not compatible with type K#2, or something similar.
  - I’m getting a strange autograder error!
Tips

The due date for this project is 02/16, but to keep you on track we have anextra credit checkpoint on 02/05 that will be a smaller version of theautograder for the project. More details later in the spec.

You will also push your snaps-sp21-s*** repo at the end of the assignment toget your Gradescope score into Beacon. More on that later.

Recall you can only use 2 slip days on this project because of thedependency between Project 1 and Lab 4.

Introduction

In Project 1, we will build implementations of a “Double Ended Queue” usingboth lists and arrays in a package that other classes can use. The projectis roughly split into two halves: the data structure portion and the applicationportion.

In the data structure part of the project, you will create two Java files:LinkedListDeque.java and ArrayDeque.java, with public methods listedbelow. You will be verifying the correctness of these data structures yourselfusing the randomized and timing test skills you gained from Lab 3.

In the application part of this project, you’ll create a Java fileMaxArrayDeque.java as well as use your package to ultimately implement a sound synthesizer capable of playing music from Guitar Hero.You must test your MaxArrayDeque, but we’ll provide the tests for soundsynthesizer.

We will provide relatively little scaffolding. In otherwords, we’ll say what you should do, but not how.

For this project, you must work alone! Please carefully read the Policy onCollaboration and Cheating to see whatthis means exactly.

Additionally, we will be enforcing style. You must follow the style guide or you will lose points on the autograder.

Getting the Skeleton Files

As with Project 0, you should start by downloading the skeleton files.

To do this, head to the folder containing your copy of your repository. Forexample, if your login is ‘s101’, then head to the ‘sp21-s101’ folder (or anysubdirectory).

To make sure you have the latest copy of the skeleton files, use the command:

git pull skeleton master

If you’re using a newer version of git, you might need to run:

git pull skeleton master -allow-unrelated-histories

You should now see a proj1 directory appear with two folders:

 proj1├── deque│ └── LinkedListDequeTest.java└── gh2 ├── GuitarHeroLite.java ├── GuitarPlayer.java ├── GuitarString.java ├── TTFAF.java └── TestGuitarString.java

If you get some sort of error, STOP and either figure it out by carefullyreading the git guide or seek help at OH or Ed. You’ll potentially saveyourself a lot of trouble vs. guess-and-check with git commands. If you findyourself trying to use commands recommended by Google like force push,don’t. Don’tuse force push, even if a post you found on Stack Overflow says to do it!

The only provided files in the skeleton are the deque/LinkedListDequeTest.javafile as well as some skeleton for the second part of this project located inthe gh2 folder (guitar hero 2).The deque/LinkedListDequeTest.java file provides examples of how you mightwrite tests to verify the correctness of your code. We strongly encourage youtry out the given tests, as well as to write your own, as these tests arenot comprehensive.

The tests in this file are also the exact tests that will be used in thecheckpoint to assess your progress on your LinkedListDeque implementation,but we will also have additional tests for ArrayDeque that we do not give you.More details on the appear checkpoint later in the spec.

Before we get into the details of the Deque API and the implementationrequirements, let’s briefly talk about packages and why we are using themin this project.

Packages

Part of this project is using packages to separate logic and functionality.At the end of the project, you’ll have two packages: the deque package thatprovides an implementation of the Deque data structure, and the gh2 packagethat implements a synthesizer used to play guitar hero. You should already seefolders with these names in the starter code, and your job is to implement them.Let’s look at the specifics for what a package really is.

A package is a collection of Java classes that all work together towards somecommon goal. We’ve already seen packages in CS 61B without knowing it. For example,org.junit is a package that contains various classes useful for testing,including our familiar Assert class, which contains useful static methods likeassertEquals. In other words, when we saw org.junit.Assert.assertEquals, theorg.junit was the package name, Assert was the class name, andassertEquals was the method name. We call org.junit.Assert.assertEquals the“canonical name” of the method, and we call assertEquals the “simple name” ofthe method.

When creating a package, we specify that code is part of a package by specifyingthe package name at the top of the file using the package keyword. For example,if we wanted to declare that a file is part of the dequepackage, we’d add the following line to the top of the file.

package deque;

If a programmer wanted to use a class or method from ourdeque package, they would have to either use the fullcanonical name, e.g. deque.ArrayDeque, or alternately use importdeque.ArrayDeque, at which point they could just use the simplename ArrayDeque. So import statements just allow you to use the simplename of a class/method.

Typically, package names are the internet address of the entity writing thecode, but backwards. For example, the JUnit library is hosted at junit.org, sothe package is called org.junit.

Why are packages useful? It all boils down to that word “canonical”. As long asno two programmers use the same package name for their package, we can freelyuse the same class name in several different contexts. For example, there mightexist a class called com.hrblock.TaxCalculator, which is different fromcom.turbotax.TaxCalculator. Given the requirement to either use the fullcanonical name or to use an import, this means we’ll never accidentally use oneclass when we meant to use the other.

Conceptually, you can think of packages as being similar to different folders onyour computer. When you are building a large system, it is a good idea toorganize it into different packages.

From this point forwards, most of our code in CS 61B will be part of a package.

With that out of the way, let’s talk about the methods that a Deque should have.

The Deque API

The double ended queue is very similar to the SLList and AList classes thatwe’ve discussed in class. Here is a definition fromcplusplus.com.

Deque (usually pronounced like “deck”) is an irregular acronym of double-endedqueue. Double-ended queues are sequence containers with dynamic sizes that canbe expanded or contracted on both ends (either its front or its back).

Specifically, any deque implementation must have exactly the followingoperations:

Project Tasks

1. Linked List Deque

Note: We covered everything needed in lecture to do this part in Lectures 4and 5 (1/27 and 1/25) with the exception of Iterators, which you’ll learn aboutin lecture 11 (2/12).

Create a file called LinkedListDeque.java in your proj1/deque directory. Makesure you declare that it is in the deque package using the special packagekeyword.

As your first deque implementation, you’ll build the LinkedListDeque class,which will be Linked List based.

Your operations are subject to the following rules:

add and remove operations must not involve any looping or recursion. Asingle such operation must take “constant time”, i.e. execution time should notdepend on the size of the deque. This means that you cannot use loops that go over all/most elements of the deque.
get must use iteration, not recursion.
size must take constant time.
Iterating over the LinkedListDeque using a for-each loop should take timeproportional to the number of items.
Do not maintain references to items that areno longer in the deque. The amount of memory that your program uses at any given time must beproportional to the number of items. For example, if you add 10,000 items tothe deque, and then remove 9,999 items, the resulting memory usage should amount toa deque with 1 item, and not 10,000. Remember that the Java garbage collectorwill “delete” things for us if and only if there are no pointers to that object.

Implement all the methods listed above in “The Deque API” section.

In addition, you also need to implement:

public LinkedListDeque(): Creates an empty linked list deque.
public T getRecursive(int index): Same as get, but uses recursion.

You may add any private helper classes or methods in LinkedListDeque.java ifyou deem it necessary. If you do, please add helpful javadoc comments for yourand your TAs sake.

While this may sound simple, there are many design issues to consider, and youmay find the implementation more challenging than you’d expect. Make sure toconsult the lecture on doubly linked lists, particularly the slides on sentinelnodes: two sentineltopology,and circular sentineltopology.I prefer the circular approach. You are not allowed to use Java’s built inLinkedList data structure (or any data structure from java.util.*) in yourimplementation and the autograder will instantly give you a 0 if we detectthat you’ve imported any such data structure.

2. Array Deque

Note: We’ll have covered everything needed in lecture to do this part bylecture 7 (2/03) with the exception of Iterators, which you’ll learn about inlecture 11 (2/12).

Create a file called ArrayDeque.java in your proj1/deque directory. Again,use the package keyword to tell this file that it is part of the dequepackage.

As your second deque implementation, you’ll build the ArrayDeque class. Thisdeque must use arrays as the core data structure.

For this implementation, your operations are subject to the following rules:

add and remove must take constant time, except during resizingoperations.
get and size must take constant time.
The starting size of your array should be 8.
The amount of memory that your program uses at any given time must beproportional to the number of items. For example, if you add 10,000 items tothe deque, and then remove 9,999 items, you shouldn’t still be using an arrayof length 10,000ish. For arrays of length 16 or more, your usage factor shouldalways be at least 25%. This means that before performing a remove operation that will bring the number of elements in the array under 25% the length of the array, you should resize the size of the array down. For smaller arrays, your usage factor can bearbitrarily low.

Implement all the methods listed above in “The Deque API” section.

In addition, you also need to implement:

public ArrayDeque(): Creates an empty array deque.

You may add any private helper classes or methods in ArrayDeque.java if youdeem it necessary.

You will need to somehow keep track of what array indices hold the Deque’s front and back elements. We strongly recommend that you treat your array as circular for thisexercise. In other words, if your front item is at position zero, and youaddFirst, the new front should loop back around to the end of the array(so the new front item in the deque will be the last item in the underlyingarray). This will result in far fewer headaches than non-circular approaches.See the project 1 demoslidesfor more details.

Correctly resizing your array is very tricky, and will require some deep thought. Try drawing out various approaches by hand. It may take you quite some time to come up with the right approach, and we encourage you to debate the big ideas with your fellow students or TAs. Make sure that your actual implementation is by you alone.

Extra Credit: Checkpoint

To keep you on track for this project, we have a checkpoint due on 2/05 for 16extra credit points. The autograder for the checkpoint will test basicfunctionality of your LinkedListDeque and ArrayDeque classes: specifically,the given tests in LinkedListDequeTest.java will be used to testyour LinkedListDeque implementation, and we will use our owntests to test your ArrayDeque implementation. By “basic functionality”, wemean all the add methods, all the remove methods, the size method, theisEmpty method, and theget method. This means we will not test your equals(Object o) nor youriterator() methods.

NOTE: the isEmpty has been on the grader the whole time but we added thisto the spec today (2/5). However, if you made the size method, this methodshould be a piece of cake (you can make it a one-liner).

Importantly, we will insertno more than 8 items in your ArrayDeque, meaning you shouldn’t have toworry about resizing for this checkpoint.

You may choose not to do the checkpoint, but we highly suggest you do sothat you stay on track and earn some extra credit while you’re at it.

The rest of the assignment will not be considered in the checkpoint.

Testing

Testing is an important part of code writing in industry and academia. It is anessential skill that can prevent monetary loss and hazardous bugs in industry,or in your case, losing points. Learning how to write good, comprehensive unittests, and developing a good habit of always testing code before shipping aresome core objectives of CS 61B.

In the start code, we have provided you a very simple sanity check,LinkedListDequeTest.java. To use the sample testing file, you must uncommentthe lines in the sample tests. Only uncomment a test once you have implementedall of the methods used by that test (otherwise it won’t compile). Execute themain method to run the tests. When testing your project, remember you can usethe visualizer from inside IntelliJ!

You will not submit LinkedListDequeTest.java. It is for your benefit to writemore comprehensive tests for both LinkedListDeque and ArrayDeque beforesubmitting. Note, passing the given tests in LinkedListDequeTest.java doesnot necessarily mean that you will pass all of the autograder tests orreceive full credit on the full autograder

Because the part of the goals for this project is for you to build something and assess thecorrectness by yourself, we do not want you to become to reliant on the fullautograder to verify correctness. Thus, you will receive one autograder tokenthat recharges every 8 hours. You cannot “stack” these tokens, so if you donot submit anything to the autograder for 3 days, you still only have one token.

On Saturday 2/13, the recharge rate will permanently reduce to every 20 minutes.

So how do you verify correctness of your data structure? You use your skillsthat you got from Lab 3! You are encouraged to copy and paste those tests forSList and AList and adapt them for these data structures. The tests willlook very similar and only require basic changes.

While it does seem very daunting and scary to do an entire project with veryminimal access to the autograder, you should feel very confident in yourimplementation if your randomized tests are really big. With just a few linesof code, you could test your data structures with sizes in the 100,000’s andall sorts of random method calls in random order. In other words, you aretesting a whole lot of cases on your data structures and are likely testingevery possible edge case! This is the beauty of randomized testing: it allowsus to leave the creativity of thinking of edge cases to randomness.

The tests you create will not be graded, but there is an additional extracredit portion of this project in which you will write your own autograder.Details near the bottom of the spec.

Your code will not compile on the full autograder until you implement the Dequeinterface and all of the required methods. So if you’ve done everything onthe spec up until this point, you should be using the checkpoint grader andnot the full grader.

Extra Credit: Autograder

For 32 points of extra credit, you can create your own autograder for deques!Full details are on this spec (to avoid cluttering this one). Itis due the same day as Project 1 (2/16). You can use slip days on extra creditassignments, but understand that staff will prioritize the required portionswhen helping students on Ed and in Office Hours. We don’t suggest working onthis extre credit assignment until you’ve finished the entire project, so keepthis in mind but continue with the assignment for now.

MaxArrayDeque

After you’ve fully implemented your ArrayDeque and tested its correctness, youwill now build the MaxArrayDeque. A MaxArrayDeque has all of the methodsthat an ArrayDeque has, but it also has 2 additional methods and a newconstructor:

Deque Interface

In the last part of this project, we’re actually going to use the data structureyou made to solve a real world problem.

Recall that we defined the Deque API, or behavior, by the following methods:

public void addFirst(T item)public void addLast(T item)public boolean isEmpty()public int size()public void printDeque()public T removeFirst()public T removeLast()public T get(int index)

Since your program will rely on this behavior, it shouldn’t matter to it what Deque implementation it is provided, ArrayDeque or LinkedListDeque, and should work for both. To achieve this, we will use the power of interfaces.

This first task is going to be a little tedious, but it won’t take long.

Create an interface in a new file named Deque.java that contains all of themethods above.In IntelliJ, use “New → Java Class”. IntelliJ will assume you want a class, so makesure to replace the class keyword with interface. Don’t forget to declare thatthe Deque interface is part of the deque package!

Modify your LinkedListDeque and/or ArrayDeque so that they implement the Dequeinterface by adding implements Deque<T> to the line declaring the existence of theclass. If IntelliJ yells at you with an error message like:

The method ... of type LinkedListDeque has the same erasure as ... of type Deque but does not override it.

It means you forgot the generic T in the implements line (i.e. you wroteimplements Deque instead of implements Deque<T>).

If you used something other than T for your generic type parameter, usethat instead. Add @Override tags to each method that overrides a Deque method.

Now, in the Deque interface, give isEmpty() a default implementation, which returns true if the size() is 0.Since your LinkedListDeque and ArrayDeque implement the Deque interface, given the default isEmpty() implementation, you can remove that method from the LinkedListDeque and ArrayDeque that you implemented earlier.

Now, after you’ve implemented the Deque interface and removed the isEmpty()method from your LinkedListDeque and ArrayDeque implementations, your codewill compile on the full autograder.

Guitar Hero

In this part of the project, we will create another package for generatingsynthesized musical instruments using the deque package we just made. We’ll get the opportunity to use our data structure for implementing an algorithmthat allows us to simulate the plucking of a guitar string.

The GH2 Package

The gh2 package has just one primary component that you will edit:

GuitarString, a class which uses an Deque<Double> to implement theKarplus-Strong algorithmto synthesize a guitar string sound.

We’ve provided you with skeleton code for GuitarString which is where youwill use your deque package that you made in the first part of this project.

GuitarString

We want to finish the GuitarString file, which should use the deque package toreplicate the sound of a plucked string. We’ll be using the Karplus-Strongalgorithm, which is quite easy to implement with a Deque.

The Karplus-Algorithm is simply the following three steps:

Replace every item in a Deque with random noise (double valuesbetween -0.5 and 0.5).
Remove the front double in the Deque and average it with the nextdouble in the Deque (hint: use removeFirst) and get()) multipliedby an energy decay factor of 0.996 (we’ll call this entire quantitynewDouble). Then, add newDouble to the back of the Deque.
Play the double (newDouble) that you dequeued in step 2. Go back to step2 (and repeat forever).

Or visually, if the Deque is as shown on the top, we’d remove the 0.2,combine it with the 0.4 to form 0.2988, add the 0.2988, and play the 0.2.

You can play a double value with the StdAudio.play method. For exampleStdAudio.play(0.333) will tell the diaphragm of your speaker to extend itselfto 1/3rd of its total reach, StdAudio.play(-0.9) will tell it to stretch itslittle heart backwards almost as far as it can reach. Movement of the speakerdiaphragm displaces air, and if you displace air in nice patterns, thesedisruptions will be interpreted by your consciousness as pleasing thanks tobillions of years of evolution. See thispage for more. If you simplydo StdAudio.play(0.9) and never play anything again, the diaphragm shown inthe image would just be sitting still 9/10ths of the way forwards.

Complete GuitarString.java so that it implements steps 1 and 2 of theKarplus-Strong algorithm. Note that you will have to fill you Deque buffer with zeros in the GuitarString constructor. Step 3 will be done by the client of theGuitarString class.

Make sure to open your project with Maven, as usual, otherwise IntelliJwon’t be able to find StdAudio.

For example, the provided TestGuitarString class provides a sample testtestPluckTheAString that attempts to play an A-note on a guitar string. If you run the testshould hear an A-note when you run this test. If you don’t, you should try thetestTic method and debug from there. Consider adding a print or toStringmethod to GuitarString.java that will help you see what’s going on betweentics.

Note: we’ve said Deque here, but not specified which Deque implementationto use. That is because we only need those operations addLast, removeFirst,and get and we know that classes that implement Deque have them. So youare free to choose either the LinkedListDeque for the actual implementation,or the ArrayDeque. For an optional (but highly suggested) exercise, thinkabout the tradeoffs with using one vs the other and discuss with your friendswhat you think the better choice is, or if they’re both equally fine choices.

GuitarHeroLite

You should now also be able to use the GuitarHeroLite class. Running it willprovide a graphical interface, allowing the user (you!) to interactively play soundsusing the gh2 package’s GuitarString class.

The following part of the assignment is not graded.

Consider creating a program GuitarHero that is similar to GuitarHeroLite,but supports a total of 37 notes on the chromatic scale from 110Hz to 880Hz. Usethe following 37 keys to represent the keyboard, from lowest note to highestnote:

String keyboard = "q2we4r5ty7u8i9op-[=zxdcfvgbnjmk,.;/' ";

This keyboard arrangement imitates a piano keyboard: The “white keys” are on theqwerty and zxcv rows and the “black keys” on the 12345 and asdf rows of thekeyboard.

The ith character of the string keyboard corresponds to a frequency of $440\cdot 2^{(i - 24) / 12}$, so that the character ‘q’ is 110Hz, ‘i’ is 220Hz, ‘v’is 440Hz, and ‘ ‘ is 880Hz. Don’t even think of including 37 individualGuitarString variables or a 37-way if statement! Instead, create an array of 37GuitarString objects and use keyboard.indexOf(key) to figure out which key wastyped. Make sure your program does not crash if a key is pressed that does notcorrespond to one of your 37 notes.

Just For Fun: TTFAF

Once you’re relatively comfortable that GuitarString should be working, tryrunning TTFAF. Make sure your sound is on!

You can read the GuitarPlayer and TTFAF classes to figure out how they work.TTFAF in particular includes (as commented-out code) an example of how to useit another way.

Even More Fun

This part of the assignment is not graded and just for fun.

Harp strings: Create a Harp class in the gh2 package. Flipping the sign of the new value before enqueueing it in tic()will change the sound from guitar-like to harp-like. You may want to play withthe decay factors to improve the realism, and adjust the buffer sizes by afactor of two since the natural resonance frequency is cut in half by thetic() change.
Drums: Create a Drum class in the gh2 package. Flipping the sign of a new value with probability 0.5 beforeenqueueing it in tic() will produce a drum sound. A decay factor of 1.0 (nodecay) will yield a better sound, and you will need to adjust the set offrequencies used.
Guitars play each note on one of 6 physical strings. To simulate this you candivide your GuitarString instances into 6 groups, and when a string isplucked, zero out all other strings in that group.
Pianos come with a damper pedal which can be used to make the stringsstationary. You can implement this by, on iterations where a certain key(such as Shift) is held down, changing the decay factor.
While we have used equal temperament, the ear finds it more pleasing whenmusical intervals follow the small fractions in the just intonation system.For example, when a musician uses a brass instrument to play a perfect fifthharmonically, the ratio of frequencies is 3/2 = 1.5 rather than 27/12 ∼ 1.498.Write a program where each successive pair of notes has just intonation.

Why It Works

The two primary components that make the Karplus-Strong algorithm work are thering buffer feedback mechanism and the averaging operation.

The ring buffer feedback mechanism. The ring buffer models the medium (astring tied down at both ends) in which the energy travels back and forth.The length of the ring buffer determines the fundamental frequency of theresulting sound. Sonically, the feedback mechanism reinforces only thefundamental frequency and its harmonics (frequencies at integer multiples ofthe fundamental). The energy decay factor (.996 in this case) models theslight dissipation in energy as the wave makes a round trip through thestring.
The averaging operation. The averaging operation serves as a gentle low-passfilter (which removes higher frequencies while allowing lower frequencies topass, hence the name). Because it is in the path of the feedback, this hasthe effect of gradually attenuating the higher harmonics while keeping thelower ones, which corresponds closely with how a plucked guitar stringsounds.

Submission and Grading

To submit the project, add and commit your files, then push to your remoterepository. Then on Gradescope go to the assignment and submit there.

After your final submission on Gradescope, you must push your snaps repo.

Your Gradescope score will not be transferred to Beacon until you’ve pushedyour snaps repo and submitted to the Snaps Gradescope assignment. To push your snaps repo, run these commands:

cd $SNAPS_DIRgit push

After you’ve pushed your snaps repository, there is a Gradescope assignmentthat you will submit your snaps-sp21-s*** repository to (similar to Lab 1A).This is only for the full grader (not the checkpoint nor the extra creditassignment).

You can do this up to a week after the deadline as well in case you forget.If you forget to push after a week, then you’ll have to use slip days.

NOTE: we slightly edited the above snaps thing as of 2/07 from simply pushingyour snaps repo to pushing and submitting on Gradescope so it’s more obvious foryou, the student, that your submission went through.

The entire project is worth 640 points

deque/LinkedListDeque: 230 points
deque/ArrayDeque: 230 points
deque/MaxArrayDeque: 80 points
gh2/GuitarString: 80 points

And there are a total of 48 extra credit points available:

Full points on the checkpoint (16 points)
Making an autograder (32 points)

Frequently Asked Questions

Deque

Q: How should I print the items in my deque when I don’t know their type?

A: It’s fine to use the default String that will be printed (this string comesfrom an Object’s implementation of toString(), which we’ll talk more aboutlater this semester). For example, if you called the generic type in yourclass Jumanji, to print Jumanji j, you can call System.out.print(j).

Q: I can’t get Java to create an array of generic objects!

A: Use the strange syntax we saw in lecture,i.e. T[] a = (T[]) new Object[1000];. Here, T is a generic type, it’s a placeholder for otherObject types like “String” or “Integer”.

Q: I tried that but I’m getting a compiler warning?

A: Sorry, this is something the designers of Java messed up when they introducedgenerics into Java. There’s no nice way around it. Enjoy your compiler warning.We’ll talk more about this in a few weeks.

Q: How do I make my arrows point to particular fields of a data structure?

In your diagram from lecture it looked like the arrows were able to point to themiddle of an array or at specific fields of a node.

A: Any time I drew an arrow in class that pointed at an object, the pointer was tothe ENTIRE object, not a particular field of an object. In fact it isimpossible for a reference to point to the fields of an object in Java.

Guitar Hero

I’m getting a “class file contains wrong class” error.

Make sure all of your Java files have the right package declaration at the top.Also make sure that anything that is part of the gh2package is in a folder called “gh2”.

I’m getting a message that I did not override an abstract method, but I am!

Chances are you have a typo. You should always use the @Override tag whenoverriding methods so that the compiler will find any such typos.

When I try to run the provided tests I get “No runnable methods”.

Make sure you’ve uncommented the tests, including the @Test annotation.

When I try to compile my code, it says type K#1 is not compatible with type K#2, or something similar.

If you’re defining an inner class, make sure it does not redeclare a new generictype parameter, e.g. the first <Z> given in private class MapWizard<Z>implements Iterator<Z>{ should not be there!

I’m getting a strange autograder error!

While GuitarString is a guitar string simulator, it should not involve playingany sounds. The playing should be done by the GuitarString client.

Credits: RingBuffer figures fromwikipedia. This assignmentadapted from Kevin Wayne’s GuitarHeroine assignment.

Tips

Check out the project 1slidesfor some additional visually oriented tips.
If you’re stuck and don’t even know where to start: One great first step isimplementing SLList and/or AList. For maximum efficiency, work with a friend or two or three.
Take things a little at a time. Writing tons of code all at once is going tolead to misery and only misery. If you wrote too much stuff and feeloverwhelmed, comment out whatever is unnecessary.
If your first try goes badly, don’t be afraid to scrap your code and startover. The amount of code for each class isn’t actually that much (my solutionis about 130 lines for each .java file, including all comments andwhitespace).
For ArrayDeque, consider not doing resizing at all until you know your codeworks without it. Resizing is a performance optimization (and is required forfull credit).
Work out what your data structures will look like on paper before you tryimplementing them in code! If you can find a willing friend, have them givecommands, while you attempt to draw everything out. Try to come up withoperations that might reveal problems with your implementation.
Make sure you think carefully about what happens if the data structure goesfrom empty, to some non-zero size (e.g. 4 items) back down to zero again, andthen back to some non-zero size. This is a common oversight.
Sentinel nodes make life much easier, once you understand them.
Circular data structures may take a little while to understand, but make life much easier for both implementations (butespecially the ArrayDeque).
Consider a helper function to do little tasks like compute array indices. Forexample, in my implementation of ArrayDeque, I wrote a function called intminusOne(int index) that computed the index immediately “before” a givenindex.
Consider using the Java Visualizer (which you installed in lab2setup) to visualize your Deque as you step through with the debugger. The visualizer is an icon of a blue coffee cup with an eye, and is the tab next to the “Console” tab in the debugger panel). See the CS 61B plugin guideif you can’t figure out how to get the visualizer to show. The visualizer will look something like this:

Project 1: Data Structures | CS 61B Spring 2021 (2024)

Introduction

Getting the Skeleton Files

Packages

The Deque API

Project Tasks

1. Linked List Deque

2. Array Deque

Extra Credit: Checkpoint

Testing

Extra Credit: Autograder

MaxArrayDeque

Deque Interface

Guitar Hero

The GH2 Package

GuitarString

GuitarHeroLite

Just For Fun: TTFAF

Even More Fun

Why It Works

Submission and Grading

Frequently Asked Questions

Deque

Q: How should I print the items in my deque when I don’t know their type?

Q: I can’t get Java to create an array of generic objects!

Q: I tried that but I’m getting a compiler warning?

Q: How do I make my arrows point to particular fields of a data structure?

Guitar Hero

I’m getting a “class file contains wrong class” error.

I’m getting a message that I did not override an abstract method, but I am!

When I try to run the provided tests I get “No runnable methods”.

When I try to compile my code, it says type K#1 is not compatible with type K#2, or something similar.

I’m getting a strange autograder error!

Tips