Problem Set 2: Multi-Startup Set

Problems 1-3: we will implement the interval set abstract type, a mutable set of unique labels where each label is associated with a non-overlapping interval on the number line.

For example, we can picture the interval set { A = [0,5), B = [10,30), C = [30,35) } as:

In this example, the labels are the unique String objects "A", "B", and "C"; and each is associated with an interval, which in our type will be an interval of long values. Every interval is half-open (also called half-closed), meaning that it includes its start point but not its end point, so [0,5) represents { x ∈ ℝ | 0 ≤ x < 5 }.

Read the Javadoc documentation for IntervalSet generated from src/​interval/​IntervalSet.java.

Labels do not have to have String type, but can have any immutable type. IntervalSet<L> is a generic type similar to List<E> or Map<K,V>. In the specification of List, E is a placeholder for the type of elements in the list. In Map, K and V are placeholders for the types of keys and values. Only later does the client of List or Map choose particular types for these placeholders by constructing, for example, a List<Clown> or a Map<Car,Integer>.

The specification of a generic type is written in terms of the placeholders. For example, the specification of Map<K,V> says that K must be an immutable type: if you want to make something the key in a Map, it shouldn’t be a mutable object because the Map may not work correctly.

In our specification for IntervalSet<L>, we make the same demand about the immutability of type L. Clients of IntervalSet who try to use mutable labels have violated the precondition. They cannot expect correct behavior.

For this problem set, we will implement IntervalSet twice, with two different reps, to practice choosing abstraction functions and rep invariants and preventing rep exposure. There are many good reasons for a library to provide multiple implementations of a type (for example, the ArrayList and LinkedList implementations of List satisfy clients with different performance requirements), and we’re following that model.

Problem 4: using interval sets, we will implement the multi-interval set type, a mutable set of labels where each label is associated with one or more globally-non-overlapping intervals.

For example, { A = [[0,5),[20,25)], B = [[10,20),[25,30)], C = [[30,35)] }:

Once again, the labels are "A", "B", and "C". Label "C" is associated with one interval, labels "A" and "B" each with two.

Read the Javadoc documentation for MultiIntervalSet generated from src/​interval/​MultiIntervalSet.java.

Problem 5: with our multi-interval set datatype in hand, the MVP for your new “” startup needs one crucial piece of proprietary technology — a way to measure the similarity between multi-interval sets.

For example, given { A = [[0,5),[20,25)], B = [[10,20),[25,30)] } and { A = [[20,35)], B = [[10,20)], C = [[0,5)] }:

We might consider an interval completely similar (value 1) when the labels are equal (e.g. on [10,20) and [20,25)) and dissimilar (value 0) otherwise.

Similarity will be defined as a ratio of the extent spanned by the two multi-interval sets, so the similarity between these two sets with the binary definition of label similarity is:

( 5×0 + 5×0 + 10×1 + 5×1 + 5×0 + 5×0 ) ÷ ( 35 - 0 ) = 15 / 35 ≈ 0.42857

(Hover or tap on individual terms to highlight that part of the figure above.)

However, our Similarity type will support a client-supplied definition of label similarity, so for example the user might specify that "A" and "C" have similarity 0 but "A" and "B" are closer, similarity ½. Using that definition:

( 5×0 + 5×0 + 10×1 + 5×1 + 5×0.5 + 5×0 ) ÷ ( 35 - 0 ) = 17.5 / 35 = 0.5

Clients of Similarity define label similarity by providing a file: for each pair of labels in the file, the client specifies a numeric similarity between 0 and 1. The similarity between all other pairs of labels is 0.

Read the Javadoc documentation for Similarity generated from src/​startup/​Similarity.java. The file format is specified in the Similarity(File) constructor Javadoc.

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For RepMapIntervalSet, you must use the rep provided:

private final Map<String, Long> startMap = new HashMap<>();
private final Map<String, Long> endMap = new HashMap<>();

You may not add fields to the rep or choose not to use one of the fields. You must use the names startMap and endMap, even if they are not the names you would choose.

Be sure to use the @Override annotation on toString to ensure that you are correctly overriding the Object version of the method, not creating a new, different method.

You should strengthen the spec of RepMapIntervalSet.toString() and write tests for it in RepMapIntervalSetTest.java. Don’t add those tests to IntervalSetTest, which must test the IntervalSet spec.

All Java classes inherit Object.toString() with its very underdetermined spec. IntervalSet doesn’t specify a stronger spec, but your concrete classes can. The choice not to strengthen the spec of toString in the IntervalSet interface is deliberate: since toString is intended for human consumption, keeping its spec weak helps prevent other code from depending on its particular format.

Run the tests by right-clicking on RepMapIntervalSetTest.java and selecting Run As → JUnit Test.

Commit to Git. Once you’re happy with your solution to this problem, commit and push!

For RepListIntervalSet, you must use the rep provided:

private final List<String> labelList = new ArrayList<>();
private final List<Long> valueList = new ArrayList<>();

You may not add fields to the rep or choose not to use one of the fields. You must use the names labelList and valueList, even if they are not the names you would choose.

You should strengthen the spec of RepListIntervalSet.toString() and write tests for it in RepListIntervalSetTest.java. Don’t add those tests to IntervalSetTest, which must test the IntervalSet spec.

Run the tests by right-clicking on RepListIntervalSetTest.java and selecting Run As → JUnit Test.

Commit to Git. Once you’re happy with your solution to this problem, commit and push!

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1. Change the declarations of your concrete classes to read:

   public class RepMapIntervalSet<L> implements IntervalSet<L> { ... }

   and:

   public class RepListIntervalSet<L> implements IntervalSet<L> { ... }

2. Update both of your implementations to support any type of label, using placeholder L instead of String. Roughly speaking, you should be able to find-and-replace all the instances of String in your code with L!

   This refactoring will make RepMapIntervalSet and RepListIntervalSet generic types.

   Any place you previously referred to these types without a generic parameter, you will need to add it. For example, if you called a constructor like new RepMapIntervalSet(), that will need to become new RepMapIntervalSet<String>(). Depending on context, you can use diamond notation <> to avoid writing type parameters twice.

   When you’re done with the conversion, all your instance method tests should pass.

Commit to Git. As always, once you’re happy with your solution to this problem, commit and push!

Because the implementation of IntervalSet does not know or care about the actual type of the labels, and only compares them according to the IntervalSet specification, your test suite with String labels is sufficient.

However, since this is our first generic type, to gain confidence that you do indeed support different types of labels, modify or add to your tests of toString() in RepMap- and RepList­IntervalSetTest so that they create and use RepMap- and RepList­IntervalSet instances (respectively) with a couple different types of (immutable) labels.

Note: you cannot write tests with other types of labels in IntervalSetTest, because those tests must use the emptyInstance() method to get new sets. That method returns IntervalSet<String>.

Pick one of your IntervalSet implementations for clients to use, and implement IntervalSet.empty(). Unlike ArrayList and LinkedList, where clients who only want a List are forced to break the abstraction barrier by calling a concrete constructor, clients of IntervalSet should not be aware of how we’ve implemented it.

At this point, all of your interval set code (implementations and tests) must have no warnings from the compiler (warnings have a symbol, as opposed to the for errors) and no @SuppressWarnings annotations (which would disable the warning, nice try).

If you cannot figure out how to make your implementations generic while satisfying the Java compiler’s static type checking, please visit lab or office hours, or ask a question on Piazza.

At this point in the problem set, we’ve completed the test-first implementation of IntervalSet.

• RepMap- and RepListIntervalSetTest should have a green bar from JUnit and excellent code coverage from the coverage tool.

• This is a good opportunity for self code review: remove dead code and debugging printlns, DRY up duplication, and so on.

• And of course, commit and push.

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Devise, document, and implement tests for MultiIntervalSet in MultiIntervalSetTest.java.

Implement MultiIntervalSet in MultiIntervalSet.java.

You must use IntervalSet in the rep of MultiIntervalSet. For example, IntervalSet instances might be elements in a list or values in a map. Your MultiIntervalSet should rely only on the specs of IntervalSet, not on the details of a particular IntervalSet implementation, and it should use the static empty() method to obtain interval set instances. The implementation of MultiIntervalSet is otherwise entirely up to you.

Run all the IntervalSet and MultiIntervalSet tests by right-clicking on the interval package in the test folder and selecting Run As → JUnit Test.

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Devise, document, and implement tests for Similarity in SimilarityTest.java.

You decide whether Similarity is mutable or immutable, and you should modify the class Javadoc to state that part of the spec.

In the future, every immutable type you write will override equals and hashCode to implement the Object contract as described in class 15 on equality, but that’s not required for this problem set.

You are free to add additional methods to Similarity, but you may not change the signatures of the required methods. You are free to strengthen the specifications of the required methods, but you may not weaken them. Note how this might mean your tests for Similarity are not usable against someone else’s implementation, because you’ve strengthened or added to the spec.

Your tests should make use of one or more sample definition files. Put those files in the test/startup directory — the same directory as SimilarityTest.java. Reference them in the code with, for example:

new File("test/startup/.txt")

While you still must test and implement Similarity(File), remember that you may add operations to Similarity. Adding a creator that takes a String or Map, for example, might simplify your tests for similarity(..).

Implement Similarity in Similarity.java.

Your Similarity type should rely only on the specs of MultiIntervalSet, not on the details of any particular implementation.

The implementation of Similarity is entirely up to you.

For reading in the label similarity definition files, there are at least three Java APIs to consider:

• FileReader is the standard class for reading from a file. Wrapping the FileReader in a BufferedReader allows you to use the convenient readLine() method to read whole lines at a time.

• The utility function Files.readAllLines(..) will read all the lines from a Path. Our constructor takes a File, but File provides a toPath() method to obtain a Path.

• Class Scanner is designed for breaking up input text into pieces. It provides many features and you’ll need to read its specs carefully.

Run all the tests in the project by right-clicking on the test folder and selecting Run As → JUnit Test.

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