Java Oops Concept:
1. Objects
2. Class
3. Inheritance
4. Polymorphism
5. Abstraction
6. Encapsulation
Object :
Any entity that has state and behaviour is known as an Object.
An object can be defined as an instance of a class.
Example :
Object = {property 1: value1, property 2: value 2……property n: value n}
Class :
- Collection of object is called class.
- It is a logical entity
- Class doesn’t consume any space.
- A class can also be defined as a blueprint from which you can create an individual object.
Inheritance :
When one object acquires all the properties and behaviours of a parent object, it is known as inheritance.
It provides code reusability.
It is a used to achieve runtime polymorphism.
Polymorphism :
If one task is performed in different way, it is known as polymorphism.
In java we use method overloading and method overriding.
Abstraction :
Hinding internal details and showing functionality is known as abstraction.
Encapsulation :
Binding or wrapping code and data together into a single unit are known as encapsulation.
Naming Convention :
1. Class
. It should start with the uppercase letter.
It should be a noun such as Color, Button, System, Thread, etc.
Use appropriate words, instead of acronyms.
Example :
Public class Employee {
//code snippet
}
2. Interface
It should start with the uppercase letter.
It should be an adjective such as Runnable, Remote, ActionListener.
Use appropriate words, instead of acronyms.
Example :
Interface Printable
{
//code snippet
}
3. Method
It should start with lowercase letter.
It should be a verb such as main(), print(),
println().
If the name contains multiple words, start it
with a lowercase letter followed by an uppercase letter such as
actionPerformed().
Example :
Class Employee
{
//method
Void get( )
{
//code snippet
}
}
4. Variables
It should start with a lowercase letter such as id, name.
It should not start with the special characters like & (ampersand), $ (dollar), _ (underscore).
If the name contains multiple words, start it with the lowercase letter followed by an uppercase letter such as firstName, lastName.
Avoid using one-character variables such as x, y, z.
Example :
Class Employee
{
// variables
Int id;
Char name;
}
5. Package
It should be a lowercase letter such as java, lang.
If the name contains multiple words, it should
be separated by dots (.) such as java.util, java.lang.
Example :
Package com.abc.xyz;
Class employee
{
//code
}
6. Constant
It should be in uppercase letters such as RED, YELLOW.
If the name contains multiple words, it should be separated by an underscore(_) such as MAX_PRIORITY.
It may contain digits but not as the first letter.
Example :
Class Employee
{
//constant
Static final int MIN_Age = 18;
//code
}
Object and class Example:
Public class Student {
Int id ;
String name;
Public static void main (String[] args)
{
Student s1 = new Student();
System.out.println(s1.id);
System.out.println(s1.name);
}
}
Syntax of class :
Class <class_name>{
Field;
Method;
}
Class Student {
Int rollno;
String name;
Void insertRecord(int r, String n)
{
Rollno = r;
Name = n;
}
Void display()
{
System.out.println(rollno+ “ “ +name);
}
Class StudentTest {
Public static void main (String[] args)
{
Student s1 = new student();
Student s2 = new Student();
S1.insertRecord(101, “Ram”);
S2.insertRecord(102, “Sita”);
S1.display();
S2.display();
}
}
Class Student {
Int id;
String name;
}
Class StudentTest {
Public static void main (String arg[])
{
Student s1 = new Student();
Student s2 = new student();
S1.id = 101;
S1.name = “Ram”;
S2.id = 102;
S2.name = “Sita”;
System.out.println(s1.id+ “ “ s1.name);
System.out.println(s2.id+ “ “ s2.name);
}
}
