An object can be defined as a section of source code that contains data and provides services. The attributes of the object are formed by the data. The services are known as methods (also known as operations or functions). Typically, it is seen that the methods operate on private data (the attributes, or state of the object), which is only visible to the methods of the object. Thus, the attributes of an object cannot be changed directly by the user, but by the methods of the object only. This guarantees the internal consistency of the object.