Using arrayList int cannot be dereferenced on error java

Question

I am getting an int cannot be dereferenced error and I'm not sure how to fix it.

public class ComparatorYearLevel implements Comparator<CourseDomain> {
    @Override
    public int compare(CourseDomain one, CourseDomain two) {
        return one.getYearLevel().compareTo(two.getYearLevel());
    }
}

Can you tell us what the meaning of the year level is, and what sorts of values it can take on? How should we be logically comparing them? — Tim Biegeleisen, Feb 17 '17 at 04:04
Your getYearLevel might be returning primitive that is not an object which yield this error as you can only comapare objects using `compareTo` method — hashmap, Feb 17 '17 at 04:21

score 0 · Answer 1 · edited May 23 '17 at 12:17

0

Here is one option:

@Override
public int compare(CourseDomain one, CourseDomain two) {
    int a = one.getYearLevel();
    int b = two.getYearLevel();
    return a > b ? 1 : a < b ? -1 : 0;
}

You could also return this:

return Integer.compare(a, b);

But the ternary expression should perform better.

Further reading: compareTo with primitives -> Integer / int

edited May 23 '17 at 12:17

Community

1
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answered Feb 17 '17 at 04:08

Tim Biegeleisen

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score -1 · Answer 2 · answered Feb 17 '17 at 04:18

Your problem is that one.getYearLevel() is returning int. Since that's not an object type, you can't go calling methods on it.

You could write

return Integer.valueOf(one.getYearLevel()).compareTo(two.getYearLevel());

This explicitly converts your int to and Integer, on which it is possible to call the compareTo method.

Another alternative would be just to write

return one.getYearLevel() - two.getYearLevel();

which meets the requirements of compareTo, provided the int values aren't large enough to risk integer overflow.

Using arrayList int cannot be dereferenced on error java

2 Answers2