Java Programming Tutorial Index

Java Object Oriented

This lesson mainly focused on Java object and class and described the features of Java object-oriented programming.

Java has following OOPS features:

In this lesson our primary focus on Objects and Classes.

What is Object?

In real-world an entity that has state and its behavior is known as an object.

For Example:

  • A Car is an object. It has states (name, color, model) and its behavior (changing gear, applying brakes).
  • A Pen is an object. Its name is Parker; color is silver etc. known as its state. It is used to write, so writing is its behavior.

In real-world object and software object have conceptually similar characteristics. In terms of object-oriented programming, software objects also have a state and behavior.

What is a class?

  • A class is a template or blueprint that is used to create objects.
  • Class representation of objects and the sets of operations that can be applied to such objects.
  • A class consists of Data members and methods.

The primary purpose of a class is to hold data/information. This is achieved with attributes which are also known as data members.

The member functions determine the behavior of the class, i.e. provide a definition for supporting various operations on data held in the form of an object.

Defining a Class in Java


public class class_name
    Data Members;


public class Car
    double color; // Color of a car
    double model; // Model of a car
  • Private, Protected, Public is called visibility labels.
  • The members that are declared private can be accessed only from within the class.
  • Public members can be accessed from outside the class also.

Class Members

Data and functions are members.

Data Members and methods must be declared within the class definition.


public class Cube
    int length; // length is a data member of class Cube
    int breadth; // breadth is a data member of class Cube
    int length ; // Error redefinition of length 
  • A member cannot be redeclared within a class.
  • No member can be added elsewhere other than in the class definition.

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