Computer Awareness Quiz: Object-Oriented Programming Concepts

Simula 67, designed by Ole-Johan Dahl and Kristen Nygaard, introduced the ideas of class, object and inheritance and is therefore treated as the first object-oriented language, from which C++ and Java later borrowed.

Recursion is a general programming technique in which a function calls itself, and it works equally well in procedural languages such as C, so it is not a feature of the object-oriented approach.

Encapsulation means binding the data members and the member functions that act on them inside one unit, the class, and keeping the data private so that it can be reached only through the methods provided; the standard illustration is a capsule holding the medicine inside it.

Abstraction presents only what the user needs, such as the accelerator and brake of a car, and keeps the internal working out of sight; in C++ it is obtained through abstract classes with pure virtual functions and in Java through interfaces and abstract classes.

Bjarne Stroustrup developed the language at Bell Laboratories, starting it as C with Classes and giving it the name C++ in 1983; it adds classes, inheritance and polymorphism to C while keeping C procedural power, which is why it is called a hybrid language.

James Gosling and his team at Sun Microsystems developed Java, which was first called Oak and was released under the name Java in 1995; its programs are compiled to bytecode and run on the Java Virtual Machine, which makes them platform independent.

Overloading means defining several functions of the same name in the same class with different numbers or types of parameters, so the compiler decides which one to call; because the decision is taken before the program runs, it is called compile-time or static polymorphism.

A class only describes the data members and member functions that its objects will have, while an object is created from the class, occupies memory and holds actual values; one class may have any number of objects.

Inheritance lets a derived, child or sub class take the members of a base, parent or super class and add its own, which is the main route to code reuse in object-oriented programming; its forms are single, multiple, multilevel, hierarchical and hybrid.

A constructor carries the same name as its class, is called automatically the moment an object is created and is normally used to give the data members their initial values; it returns no value at all, not even void, and it can be overloaded.

Java deliberately leaves out multiple inheritance of classes to avoid the ambiguity that arises when two base classes supply a member of the same name, the problem often called the diamond problem, and it provides interfaces so that a class can still take behaviour from more than one source.

Private is the most restricted access specifier and is also the default for a C++ class, so private data members can be read or changed only by the member functions of that class, and by a friend function or friend class if one is declared.