Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
Equality is supposed to be symmetric, right?
Object someObject = new Object();
Object NULL = null;
NULL.equals(someObject) => NullPointerException
someObject.equals(NULL) => false
What is the rationale for not having the second form throw a NullPointerException?
Equality is certainly defined to be symmetric in a theoretical sense, but it also isn’t defined at all on non-existent objects (which is what null represents).
Hence any behaviour when applied to null would be equally valid. It could return a live rabbit and still not contradict the theoretical definition of equality.
In such a case, it’s a pretty reasonable implementation decision on behalf of the designers of Java that calling equals on a null value should throw a NullPointerException, as that is consistent with calling any other method on a null value.