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OOP Interview Questions Answers

Question 1 : Does a class inherit the constructors of its superclass?

Answer 1 : A class does not inherit constructors from any of its super classes. If a class is declared without any access modifiers, where may the class be accessed? A class that is declared without any access modifiers is said to have package access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.

Question 2 : What is the difference between superclass and subclass?

Answer 2 : A super class is a class that is inherited whereas sub class is a class that does the inheriting.

Question 3 : Differentiate Aggregation and containment?

Answer 3 : Aggregation is the relationship between the whole and a part. We can add/subtract some properties in the part (slave) side. It won’t affect the whole part. Best example is Car, which contains the wheels and some extra parts. Even though the parts are not there we can call it as car. But, in the case of containment the whole part is affected when the part within that got affected. The human body is an apt example for this relationship. When the whole body dies the parts (heart etc) are died.

Question 4 : Differentiate persistent & non-persistent objects?

Answer 4 : Persistent refers to an object’s ability to transcend time or space. A persistent object stores/saves its state in a permanent storage system with out losing the information represented by the object. A non-persistent object is said to be transient or ephemeral. By default objects are considered as non-persistent.  

Question 5 : List out some of the object-oriented methodologies.

Answer 5 : Object Oriented Development (OOD) (Booch 1991,1994). Object Oriented Analysis and Design (OOA/D) (Coad and Yourdon 1991). Object Modeling Techniques (OMT) (Rumbaugh 1991). Object Oriented Software Engineering (Objectory) (Jacobson 1992). Object Oriented Analysis (OOA) (Shlaer and Mellor 1992). The Fusion Method (Coleman 1991).

Question 6 : What is a modifier?

Answer 6 : A modifier, also called a modifying function is a member function that changes the value of at least one data member. In other words, an operation that modifies the state of an object. Modifiers are also known as ‘mutators’. Example: The function mod is a modifier in the following code snippet: class test { int x,y; public: test() { x=0; y=0; } void mod() { x=10; y=15; } };

Question 7 : What is multithreading?

Answer 7 : Multithreading is the mechanism in which more than one thread run independent of each other within the process.

Question 8 : What are inner class and anonymous class?

Answer 8 : Inner class : classes defined in other classes, including those defined in methods are called inner classes. An inner class can have any accessibility including private. Anonymous class : Anonymous class is a class defined inside a method without a name and is instantiated and declared in the same place and cannot have explicit constructors.

Question 9 : Differentiate between a template class and class template.

Answer 9 : Template class: A generic definition or a parameterized class not instantiated until the client provides the needed information. It’s jargon for plain templates. Class template: A class template specifies how individual classes can be constructed much like the way a class specifies how individual objects can be constructed. It’s jargon for plain classes.

Question 10 : Differentiate between the message and method.

Answer 10 : Message * Objects communicate by sending messages to each other. * A message is sent to invoke a method. Method * Provides response to a message. * It is an implementation of an operation.

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