Class and object

Class

• Class is a structure.
• Binding the data with its related and corresponding functions.
• Class is the base for encapsulation.
• Class is a user defined data type in java.
• Class will act as the base for encapsulation and implement the concept of encapsulation through objects.
• Any java applications looks like collection of classes but where as c- application looks like collection of functions.

public class Example{

         //variable declaration
          int id;

      // methods
        public int getId() {
          return id;
         }

    public void setId(int id) {
        this.id = id;
    }

}

Object

• Object is nothing but instance (dynamic memory allocation) of a class.
• The dynamic memory allocated at run time for the members [non-static variables] of the class is known as object.

What is a Reference variable?

• Reference variable is a variable which would be representing the address of the object.
• Reference will act as a pointer and handler to the object.
• Since reference variable always points an object.
• In practice we call the reference variable also as an object.
• We can create an object by using new operator.
• If we want to call any method inside the class we need object

               Syntax: A obj= new A();

Example program:

      public class A {
         int a;
     public  void Print(){
        System.out.println("value of a="+a);
    }
    public static void main(String[] args) {
   A obj=new A();
  obj.print();
    }
}

Output: value of a=0
What Object Contains?

• Object of any class contains only data.
• Apart from the data object of a class would not contains anything else.
• Object of a class would not contain any functionalities or logic.
• Thus object of a class would be representing only data and not represent logic.

What is state of the Object?

• The data present inside object of a class at that point of time is known as state of the object . 

What is behavior of the object? 

• The functionalities associated with the object => Behavior of the object.

     The state of the object changes from time-to-time depending up on the functionaities that are executed on that object but whereas behavior of the object would not change.

Naming conventions for declaring a class:

• Class name should be relevant.
• Use UpperCamelCase for class names. //StudentDemoClass
• For Methods names follow camelCase(); //getName();
• Declare variables lowercase first letter. // int rollNumber
• To declare final static variables means which will acts like constants
  MIN_WIDTH=10;
  MAX_AGE=18;