1. What is an adaptor class or Wrapper class?
Ans: 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.
2. What is a Null object?
Ans: 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.
3. What is class invariant?
Ans: 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.
4. Differentiate between the message and method.
* 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.
5. What is a dangling pointer?
Ans: A dangling pointer arises when you use the address of an object after
its lifetime is over. This may occur in situations like returning
addresses of the automatic variables from a function or using the
address of the memory block after it is freed.
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