Implementation of isEmpty()

Question

I'm trying to figure some basic things out. I was exploring standard library ArrayList.java when found that ArrayList has implementation of method isEmpty().

ArrayList.java:

public boolean isEmpty() {
    return size == 0;
}

ArrayList extends AbstractList extends AbstractCollection. And AbstractCollection has implementation of isEmpty as well:

public boolean isEmpty() {
    return size() == 0;
}

I'm just trying to get the logic? Why ArrayList implements already implemented method? What for?

P.S. ArrayList also has size

public int size() {
    return size;
}

Because not every collection provides a local `size` field, and it's a *specialization* (or *optimization*) available in this case. — Elliott Frisch, Jan 15 '17 at 22:23

score 3 · Accepted Answer · answered Jan 15 '17 at 22:24

3

The ArrayList version is a minor, but effective, optimisation.

answered Jan 15 '17 at 22:24

Bathsheba

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2

[citation needed] – shmosel Jan 15 '17 at 22:25
How do you actually view the ArrayList class in eclipse? Is it somewhere in library? – Nick Ziebert Jan 15 '17 at 22:27
1

Well, I guess I figured it out now, thanks! Nick Ziebert, I was watching declarations of all I saw on screen with Alt + B. – Nederes Jan 15 '17 at 22:46

Implementation of isEmpty()

1 Answers1