ArrayList or Array? Not sure what kind of declaration this is

Question

ArrayList<Integer>[] paths = new ArrayList[N];

This line is part of a code given to me in an Assignment to use as part of Djikstra's algorithm. Since it was given to me in the assignment I assume it's syntactically correct but I don't think I've ever seen an ArrayList being declared with the brackets used to declare Arrays.

Is this an ArrayList or an Array? What do the brackets mean in this case?

@testo Because arrays have limited flexibility, and since you're already using a list (imposing a small overhead), so there is no need to also use an array. More about the subject. Also, arrays don't work well with generics. E.g. new ArrayList<T> is valid, but new T[0] isn't. — MC Emperor
– MC Emperor, Commented Feb 22, 2021 at 8:46
I would say a reason to not mix them is that it's hard to read and understand quickly... Integer[][] is easy to read and ArrayList<ArrayList<Integer>> is easy to read, but that is just confusing at first glance. — Phillip
– Phillip, Commented Feb 22, 2021 at 8:50

testo · Accepted Answer · 2021-02-22 08:33:45Z

5

An array of ArrayList-Instances.

answered Feb 22, 2021 at 8:33

testo

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score 3 · Accepted Answer · 2021-02-22 09:16:49Z

3

to be very exact (or even pedantic), it is an array with N elements:
= new ArrayList[N].

Each element itself can be an ArrayList - but after that statement, the array is just filled with nulls.

edited Feb 22, 2021 at 9:16

answered Feb 22, 2021 at 9:00

user15244370

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