isEmpty（）的实现

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?

PS ArrayList also has size

public int size() {
    return size;
}

Answer 1

ArrayList版本是次要但有效的优化。