object

object

Definition 1

• Instance of a class is known as an object
• Instance is a way of allocating the sufficient amount of memory for data members.

Definition 2

• Group of items exists in single entity is known as an object.
• We can say single entity means an object variable which holds group of values.

Definition 3

• Real world entities are called as objects.

Definition 4

• Logical run time entities are called as objects.

Bulletin points 

• An object can exists physically in this world but class does not exist.
• An object does not exist without class but class can exist without object
• Read again above statement for better understanding.
• Simply i can say object will come from class.
• Every object having state, behavior and identity of an object.
• we can create object by using new keyword.

Syntax 

         Classname objectname = new constructor();

Example:

         Student s1 = new Student();

• Classname(Student) represents the name of the class
• objectname(s1) represents any java valid variable name.
• by using new(new) operator we will create an object for class.
• If constructor(Student()) will exists in class(Student) then at the time of object creation it will be called automatically

Note

• We will learn clearly about constructor in upcoming chapter.

Why should we create an object?

• Once if you define any variable or data in java program then immediately memory will be not allocated for that data.
• If we create an object for that class then memory will be assign to the data.

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Program        :       Sample class and object program

Program name :       Demo1.java

Output           :        

                            Id is : 1

                            Name is : Mouli

class Demo1

{

        int id = 1;

        String name = "Mouli";

        public static void main(String args[])

        {

                Demo1 demo1 = new Demo1();

                System.out.println("Id is : "+demo1.id);

                System.out.println("Name is : "+demo1.name);

        }

}

Compile          :      javac Demo1.java

Run                :      java Demo1

Output            :        

                             Id is : 1

                             Name is : Mouli

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Thanks for your time.

Nireekshan