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Object and Class in Java


Before discussing OOPs concept let us have a brief look at object and class with real world examples.

Object in Real world:

A real world entity. Every real world object/entity has two characteristics state and behavior.  Let us take the example of a car. Its state is defined by color, current speed etc and behavior is defined by changing speed, applying breaks etc.

Object in programming:

Like every real world object, software objects also have state and behavior.  State of the object is represented by data members or fields and behavior is represented by methods.

object and class

 

Class in Real world:

Let us take the example of cars. There are thousands of cars in existence but all built from the same set of blueprints and therefore contains the same components. In other words your car is an instance (object) and cars is the blueprint (class of objects).

Class in programming: 

Class is act as a blue print or template for creating objects. It provides state and behavior for its objects. Java is a pure object oriented language means everything we discuss in java is an object.

 Syntax:

access_modifier class class_name{      //body of the class

}

 

Java class has mainly two type of access level:

Default: class objects are accessible only inside the package.
Public: class objects are accessible in code in any package.

Note: If no access modifier used it is taken as default.

Example:

/**
 * This class is used add and show car details.
 * @author CodesJava
 */
public class Car {
      String carColor;
      int carSpeed;  
 
      /**
       * This method is used to add car details.
       * @param color
       * @param speed
       * @author CodesJava
       */
      void addCarDetails(String color, int speed){
            carColor = color;
            carSpeed = speed;
      }     
 
      /**
       * This method is used to show details.
       * @author CodesJava
       */
      void showCarDetails(){
            System.out.println("Color: " + carColor);
            System.out.println("Speed: " + carSpeed);
      }     
 
      public static void main(String args[]){
            //creating objects
            Car car1 = new Car();
            Car car2 = new Car();           
 
            //method call, need object here
            //because method is non-static.
            car1.addCarDetails("white", 120);
            car2.addCarDetails("Red", 150);           
 
            car1.showCarDetails();
            car2.showCarDetails();
      }
}

Output:

Color: white
Speed: 120
Color: Red
Speed: 150

Download this example.
 
Next Topic: OOPs Principles/Concepts.
Previous Topic: OOPs Basics.

Related Topics:

OOPs Basics.
Object and Class in Java.
OOPs Principles/Concepts.
Abstraction in java.
Encapsulation in java.
Polymorphism in java.

 

Core Java Tutorial

Programming language overview.
Overview of Java.
Java features
JVM architecture details.
JVM, JRE and JDK.
Java Coding Guidelines.
Some important definitions.
Variable and data types.
Hello world java program.
Core java examples programs.
Important Java Programs.
How to set permanent path in java?
OOPs Basics.
Object and Class in Java.
OOPs Principles/Concepts.
Abstraction in java.
Encapsulation in java.
Polymorphism in java.
Method overloading in java.
Method overriding in java.
Dynamic method dispatch.
Runtime polymorphism.
Association in java.
Inheritance in java.
Aggregation in java.
Command line arguments in java.
Command line argument program in eclipse.
Read input from command line using Scanner.
Java array programs
Java star pattern programs
Java number pattern programs
final in java.
Abstract class in java.
Interface in java.
Custom marker Interface in java.
Constructor in java.
Package in java.
Access modifier in java.
Static import in java.
Package class in java.
this in java.
Instance initialize block.
Anonymous block.
super in java.
Static in java.
final in java.
Java cloning deep and shallow
Shallow vs Clone copy
String handling in java.
String handling programs.
StringBuffer in java.
StringBuilder in java.
Exception Handling Tutorial.
Multithreading Tutoial.
Java input output stream tutorial.
Collections framework in java tutorial.
Collections framework programs.
Java Random class
Java annotations.
Java design principles.
Java 7 features
Java 8 features
Java networking tutorial
Java Reflection tutorial
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