设计比较器的最佳方法是访问可能为空或为null的字符串字段

Question

I have to sort a Collection by different String attributes that might be empty ( "" ) or even null . Both values are allowed and have to be treated equally.

I solved this issue by using a method, that checks each String for null and returns an empty String, when null is found.

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So far my Comparator looks basicly like this

public class MyComparator implements Comparator<MyObject> {

    @Override
    public int compare(MyObject o1, MyObject o2) {
        // ... some logical stuff like e.g.
        return rein(o1.getSomeValue()).compareTo(rein(o2.getSomeValue());
    }

    private String rein(String str) {
        return str == null ? "" : str;          
    }
}

I wonder if this design is considered to be ok or if there are reason against it? If it is not ok, what else may I do to fulfil my requirements? All those (in most cases unneccessary) function calls looks ugly to me, as we are talking about approximately 1/1000 cases. So I wonder if there is a more elegant solution?

Answer 1

Nothing wrong here. If you omit 'rein' method you will get NullPointerException in case when o1.getSomeValue() returns null. So this check is necessary for correct compare method working. It's hard to imagine more elegant solution.