Java Classes & Object

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Java Classes & Object : Java is an Object-Oriented Language. As a language that has the Object-Oriented feature, Java supports the following fundamental concepts :

• Polymorphism
• Inheritance
• Encapsulation
• Abstraction
• Classes
• Objects
• Instance
• Method
• Message Passing

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In this , we will look into the concepts – Classes and Objects.

i) Object : Objects have states and behaviors. Example: A dog has states – color, name, breed as well as behaviors – wagging the tail, barking, eating. An object is an instance of a class.

ii) Class : A class can be defined as a template/blueprint that describes the behavior/state that the object of its type support.

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Objects in Java:

Let us now look deep into what are objects. If we consider the real-world, we can find many objects around us, cars, dogs, humans, etc. All these objects have a state and a behavior.

If we consider a dog, then its state is – name, breed, color, and the behavior is – barking, wagging the tail, running.

If you compare the software object with a real-world object, they have very similar characteristics.

Software objects also have a state and a behavior. A software object’s state is stored in fields and behavior is shown via methods.

So in software development, methods operate on the internal state of an object and the object-to-object communication is done via methods.

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Classes in Java:

A class is a blueprint from which individual objects are created.

Example:

public class Dog {
   String breed;
   int age;
   String color;
   void barking() {
   }
   void hungry() {
   }
   void sleeping() {
   }
}

Local variables.

Instance variables.

Class variables.

A class can have any number of methods to access the value of various kinds of methods. In the above example, barking(), hungry() and sleeping() are methods.

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Creating an Object:

As mentioned previously, a class provides the blueprints for objects. So basically, an object is created from a class. In Java, the new keyword is used to create new objects.

There are three steps when creating an object from a class :

(i) Declaration.

(ii) Instantiation.

(iii) Initialization.

Example:

public class Puppy {
   public Puppy(String name) {
      // This constructor has one parameter, <i>name</i>.
      System.out.println(“Passed Name is :” + name );
   }
   public static void main(String []args) {
      // Following statement would create an object myPuppy
      Puppy myPuppy = new Puppy( “tommy” );
   }
}

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