Java Tutorial

Java is a programming language and a platform. Java is a high level, robust, object-oriented and secure programming language.
Java was developed by Sun Microsystems (which is now the subsidiary of Oracle) in the year 1995. James Gosling is known as the father of Java. Before Java, its name was Oak. Since Oak was already a registered company, so James Gosling and his team changed the name from Oak to Java.

Creating Your First Java Program 

Create a new file in your text editor or IDE named HelloWorld.java. Then paste this code block into the file and save: 

public class HelloWorld { 
   public static void main(String[] args) { 
        System.out.println("Hello, World!");
    } 
} 

OOPS Concepts in Java

Concepts in OOPS

➔ Object 

➔ Class 

➔ Inheritance 

➔ Encapsulation 

➔ Abstraction 

➔ Polymorphism

 1. Object

➔ Any real world entity is an object. It has Behavior and Attribute. 

➔ Behavior tells what object does or performs. 

➔ Attribute is use to describe the object. 

Chair🪑 

It can be considered as an object, with behaviors like wheel movement, adjust height, recline, etc. and attributes like color, brand, price, etc.

2. Class

➔ The collection of all related objects is called Class. 

➔ Consider class as a general category which contains all the related objects inside it. 

Chair🪑 

Objects like Wheel chair, Office chair, Recliner chair belong to Chair class.

3. Inheritance

➔ In real world, a Child inherits qualities from his/her Parent. 

➔ Similarly, a Child class can also inherit qualities from it's Parent class. 

Phone 

Parent class Phone can have two child classes - 

• ☎TelePhone 
• MobilePhone 

Both these child classes can inherit the calling behavior.

4. Encapsulation

➔ It means wrapping the data into a single unit & securing it. 

➔ It secures data from the outside world. 

Bank Locker🔐 

A Banker Locker, wraps your valuables into a single unit(locker) and protects it via passcode. 

Drug Capsule💊 

Wraps different medicines into a single unit and protect them from outside environment. 

 5. Abstraction

➔ Hiding complexity from the user and showing only the relative stuff. 

➔ This enables user to only focus on relevant stuff. 

Car 

1. In car, all the complexity like engine, machinery, etc is hidden from you. 
2. Only relevant part is shown like the brakes, accelerator, and gearbox. 

 6. Polymorphism

➔ The word polymorphism means many forms. 

➔ It talks about using the same name and providing different behaviour. 

Chess 

 All chess pieces like king, rook, bishop, queen, knight, etc. move differently. Bishop moves diagonally, Rooks move horizontal and vertical, etc. 

The common behavior name "move" is the same for all pieces but it's still differently done by them which is nothing but polymorphism.