java.lang.object

[Kota li]

which of the following classes java.lang.Object override hashCode() method in Object class
java.lang.String
,, ,, .StringBuffer
.Number
.Byte
which of them override

[Jesper de Jong]

You can find the answer by looking up the API documentation of those classes. If the documentation doesn't mention a hashCode() method, then the class doesn't override it.

[Vikrant Sahdev]

String and Wrapper classes override equals() method. And by contract, if you override equals() method, you need to override hashCode()method as well.

StringBuffer doesnt override equal()method and therefore doesnt override hashCode()method as well.