You should override the hashCode() and equals() functions from the Object class. The default implementation of the hashcode() and equals(), which are inherited from the java.lang.Object needs an object instance's memory location. That can cause serious problems when two instances of the car objects have the similar color but the inherited equals() can give false because it uses the memory location, which is distinct for the two instances of object. Also the toString() method may be overridden to give a proper string representation of your object.