Java's Comparable Interface: Handling null arguments to compareTo()

Question

Writing some classes for a Framework extension, and I have the following code:

public class TimeImpl implements Time, Comparable<TimeImpl>, Serializable
{
...
    public int compareTo(TimeImpl other)
    {
        if (other == null)
            throw new ClassCastException("null");
        return Long.valueOf(toSeconds()).compareTo(other.toSeconds());
    }
}

Pretty straightforward implementation, if you ask me. My question is: as far as I can tell, the javadocs for the Comparable interface say nothing regarding null arguments. Should I bother checking for it? Should I change the type of exception thrown, should I return some other value in that case? How are other people out there handling this?

Duplicate of [How to simplify a null-safe compareTo() implementation?](http://stackoverflow.com/questions/481813/how-to-simplify-a-null-safe-compareto-implementation) — ziesemer, Jan 20 '12 at 02:00
possible duplicate of [Comparable and Comparator contract with regards to null](http://stackoverflow.com/questions/2858628/comparable-and-comparator-contract-with-regards-to-null) — Don Roby, Jan 20 '12 at 02:00

score 4 · Answer 1 · answered Jan 20 '12 at 02:04

4

Actually, the Comparable interface does say something about handling null arguments.

Note that null is not an instance of any class, and e.compareTo(null) should throw a NullPointerException even though e.equals(null) returns false.

answered Jan 20 '12 at 02:04

Jeffrey

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score 3 · Answer 2 · answered Jan 20 '12 at 02:02

3

I prefer to throw NullPointerException rather than ClassCastException.

This convention is also followed by JDK implementations.

answered Jan 20 '12 at 02:02

Gelin Luo

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score 1 · Accepted Answer · answered Jan 20 '12 at 02:04

1

The code below is the compareTo method of Integer from java:

 public int compareTo(Integer anotherInteger) 
 {
    int thisVal = this.value;
    int anotherVal = anotherInteger.value;
    return (thisVal<anotherVal ? -1 : (thisVal==anotherVal ? 0 : 1));
 }

why not implement your compareTo method in the way Integer does.

answered Jan 20 '12 at 02:04

Alanmars

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I've basically gone with something like this. Not sure why I didn't realize that invoking a method on the null pointer would throw the exception I needed, without have to explicitly check for null. – Alexandros Katechis Jan 20 '12 at 16:57

Java's Comparable Interface: Handling null arguments to compareTo()

3 Answers3