Incorrect Null Check Example in Comparator Section

[nnirmall]

Description:

The documentation on this page currently presents the following code example for a Comparator<Integer> in the Dealing with Null Values section. In this section, the author states:

Suppose you need to write a null-safe comparator of integers to sort a list of integers. The convention you decide to follow is to push all the null values at the end of your list, meaning that a null value is greater than any other non-null value. And then you want to sort non-null values in their natural order.

To illustrate this behavior, the documentation provides the following code example:

Comparator<Integer> comparator = (i1, i2) -> {
    if (i1 == null && i1 != null) {  // <-- This condition can never be true! [NOTE]
        return 1;
    } else if (i1 != null && i2 == null) {
        return -1;
    } else {
        return Integer.compare(i1, i2);
    }
};

Problem:

The condition i1 == null && i1 != null in line 3 is logically impossible and will always evaluate to false because i1 cannot be both null and not null at the same time. This block will never execute. This may confuse readers and does not demonstrate correct null handling.

Suggested Correction:

Update the example to properly handle nulls. For example:

Comparator<Integer> comparator = (i1, i2) -> {
    if (i1 == null && i2 != null) {
        return 1;
    } else if (i1 != null && i2 == null) {
        return -1;
    } else if (i1 == null && i2 == null) {
        return 0; 
    } else {
        return Integer.compare(i1, i2);
    }
};

Request:

Please update the documentation to use a correct null check example for clarity and accuracy.

[danthe1st]

I think the following (in your suggestion) is not necessary as this is handled by Integer.compare:

else if (i1 == null && i2 == null) {
    return 0; 
}

Alternatively, one could maybe try to use switch patternmatching (there you might need that option) to do that but I don't know whether readerss should know about that at that point.

[JosePaumard]

Thank you for your report! Indeed this is a rypo, I just pushed a fix.