Rec 06

Question (without answers):

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Answers:

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Problems

01. Rewrite method into one return statement using Maybe

The kind of question contains two steps:

1. Ignore any null check or equivalent (e.g. none() check)

2. Write down the actual steps that do things

3. Choose the corresponding methods

So, follow the three steps, after step 1 and 2, we should find our that in this question, there are three things we should do

1. get the list of languages (by calling r.getListofLanguages())

2. check whether the list contains "Java"

3. If so, return the wrapper of findInternship() as the method's return.

Now, moving on to step 3 — choose the corresponding API from Maybe.

1. r.getListofLanguages() will return a wrapper of "something". This tells us that we should use flatMap() instead of map()

2. "check, contains" tells us that we should use filter()

3. findInternship() will return "something", but we need to wrap it first, then return it to a function. This tells us that we should use map() instead of flatMap().

So, the final answer will be

Maybe<Internship> match(Resume r) {
    return Maybe.of(r)
        .flatMap(x -> x.getListOfLanguages())
        .filter(l -> l.contains("Java"))
        .map(l -> findInternship(l));
}

02. Stack and Heap with Lambda

In CS2030s style,

1. The lambda expression should be explicitly written in the anonymous class name

2. The captured variable should be placed under a dashed line

A a = new A(5);
Producer<Integer> p = () -> a.get();
p.produce();

So, in this question, why we have a as our captured variable? This is because according to the first rule from here:

The local variables of the method where the local class comes from will be captured.

So, in this unamed method, Line 2 is acutally creating an anonymous class (local class) inside this unamed method, and a is a local variable in this method, so, it will be captured!