java - Any reason to prefer getClass() over instanceof when generating .equals()?

Question

I'm using Eclipse to generate .equals() and .hashCode(), and there is an option labeled "Use 'instanceof' to compare types". The default is for this option to be unchecked and use .getClass() to compare types. Is there any reason I should prefer .getClass() over instanceof?

Without using instanceof:

if (obj == null)
  return false;
if (getClass() != obj.getClass())
  return false;

Using instanceof:

if (obj == null)
  return false;
if (!(obj instanceof MyClass))
  return false;

I usually check the instanceof option, and then go in and remove the "if (obj == null)" check. (It is redundant since null objects will always fail instanceof.) Is there any reason that's a bad idea?

Answer 1

Josh Bloch favors your approach:

The reason that I favor the instanceof approach is that when you use the getClass approach, you have the restriction that objects are only equal to other objects of the same class, the same run time type. If you extend a class and add a couple of innocuous methods to it, then check to see whether some object of the subclass is equal to an object of the super class, even if the objects are equal in all important aspects, you will get the surprising answer that they aren't equal. In fact, this violates a strict interpretation of the Liskov substitution principle, and can lead to very surprising behavior. In Java, it's particularly important because most of the collections (HashTable, etc.) are based on the equals method. If you put a member of the super class in a hash table as the key and then look it up using a subclass instance, you won't find it, because they are not equal.

See also this SO answer.

Effective Java chapter 3 also covers this.