Differentiate between the message and
* Objects communicate by sending messages to each other.
* A message is sent to invoke a method.
* Provides response to a message.
* It is an implementation of an operation.
What is an adaptor class or Wrapper class?
A class that has no functionality of its own. Its member functions hide
the use of a third party software component or an object with the
non-compatible interface or a non-object-oriented implementation.
What is a Null object?
It is an object of some class whose purpose is to indicate that a real
object of that class does not exist. One common use for a null object is
a return value from a member function that is supposed to return an
object with some specified properties but cannot find such an object.
What is class invariant?
A class invariant is a condition that defines all valid states for an
object. It is a logical condition to ensure the correct working of a
class. Class invariants must hold when an object is created, and they
must be preserved under all operations of the class. In particular all
class invariants are both preconditions and post-conditions for all
operations or member functions of the class.
What do you mean by Stack unwinding?
It is a process during exception handling when the destructor is called
for all local objects between the place where the exception was thrown
and where it is caught.
Define precondition and post-condition to a member function.
Precondition: A precondition is a condition that must be true on entry
to a member function. A class is used correctly if preconditions are
never false. An operation is not responsible for doing anything sensible
if its precondition fails to hold. For example, the interface invariants
of stack class say nothing about pushing yet another element on a stack
that is already full. We say that isful() is a precondition of the push
operation. Post-condition: A post-condition is a condition that must be
true on exit from a member function if the precondition was valid on
entry to that function. A class is implemented correctly if
post-conditions are never false. For example, after pushing an element
on the stack, we know that isempty() must necessarily hold. This is a
post-condition of the push operation.
What are the conditions that have to be met for a condition to be an
invariant of the class?
* The condition should hold at the end of every constructor.
* The condition should hold at the end of every mutator (non-const)
What are proxy objects?
Objects that stand for other objects are called proxy objects or
template <class t="">
T& operator (int index);
const T& operator (int index)const;
Array1D operator (int index);
const Array1D operator (int index) const;
The following then becomes legal:
cout<<data; // fine
Here data yields an Array1D object and the operator  invocation on
that object yields the float in position(3,6) of the original two
dimensional array. Clients of the Array2D class need not be aware of the
presence of the Array1D class. Objects of this latter class stand for
one-dimensional array objects that, conceptually, do not exist for
clients of Array2D. Such clients program as if they were using real,
live, two-dimensional arrays. Each Array1D object stands for a
one-dimensional array that is absent from a conceptual model used by the
clients of Array2D. In the above example, Array1D is a proxy class. Its
instances stand for one-dimensional arrays that, conceptually, do not
Name some pure object oriented languages.
Smalltalk, Java, Eiffel, Sather.
What is an orthogonal base class?
If two base classes have no overlapping methods or data they are said to
be independent of, or orthogonal to each other. Orthogonal in the sense
means that two classes operate in different dimensions and do not
interfere with each other in any way. The same derived class may inherit
such classes with no difficulty.