Object Oriented System Design : Practice Questions and Answers

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Java defines eight simple types of data which are put in four groups. They are integers, floating-point numbers, boolean, characters.

Primitive Datatypes are defined by Java. Reference Datatypes are user defined, created using defined constructors of class.

A destructor is used to destroy the objects that have been created by a constructor. Like a constructor, the destructor is a member function whose name is same as the class name but is preceded by a tilde.

A copy constructor takes reference to an object of the same class as itself as an argument.

In order to initialize the various data elements of different objects with different values when they are created parameterized constructors are used.

An object with a constructor cannot be used as a member of a union. A union is a limited form of the class type. It can contain access specifiers (public, protected, private), member data, and member functions, including constructors and destructors. It cannot contain virtual member functions or static data members. Default access of members in a union is public. A union cannot be used as a base class and cannot be derived from a base class. (same with the constructor too, constructor cannot be inherited, though a derived class can call the basic class constructor).

Constructors are special because its name is same as the class name. The constructor is invoked whenever an object of its associated class is created. It is called constructor because it constructs the value of data members of the class.

Classes are the most important building blocks of any object- oriented systems. Classes are used to capture the vocabulary of the system you are developing. Modeling a system involves identifying the things that are important to your particular view. Hence all the above mentioned properties would distinguish each class from one another.

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The above declaration denotes a class, not an object, because it does not represent a specific instance. To declare objects of this class we usually write in the following way:

PersonnelRecord deb, dave, jim, tom;

Class declaration is almost similar to struct declaration except that in reality it uses a keyword 'class' in place of 'struct.'

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An object has state, exhibits some well defined behavior, and has a unique identity.