Abstraction in Java

Abstraction in Java, Java Object-Oriented Programming, Abstract Class, Abstract Methods, Java Interfaces, and Inheriting Abstract classes.

Java Abstraction

Four principles of Java object-oriented program,

1. Inheritance
2. Polymorphism
3. Abstraction
4. Encapsulation

Java Object-Oriented Programming – Abstraction

Abstraction is a Process of hiding implementation details and showing only functionality to the user.

Two types of Methods

1. Concrete Methods (The Methods which are having body)

Syntax:

accessModifier retrunType / returnTypeNothing method Name() {
Statements
———-
———–
————-
}

2. Abstract Methods (The Methods which are not having bodies)

Syntax:

accessModifier abstract returnType / returnTypeNothing MethodName();

•  If we know the method name, but don’t know the method functionality then we go for Abstract Methods

•  Java Class contains 100% concrete Methods.

•  Abstract Class contains one or more abstract methods.

Example:

Class1 (having 10 methods)

10 Methods are concrete Methods.

It is a Java Class
——————————
Class2 (having 10 methods)

5 Methods are concrete Methods and 5 methods are abstract methods)

It is an Abstract Class
——————————–
Class3 (having 10 Methods)

All Methods are Abstract Methods

It is an Abstract Class

Example for Abstract Class:

public abstract class Bikes {

public void handle(){
System.out.println(“Bikes have Handle”);
}

public void seat(){
System.out.println(“Bikes have Seats”);
}

public abstract void engine();

public abstract void wheels();

public static void main(String[] args) {
//Bikes obj = new Bikes();

}
}

Note: We cannot create Object/Instance in Abstract Class.

Note 2: In order to use Methods from Abstract Class then first we need to implement abstract methods in sub-class.

Use methods from Abstract Class:

public class HeroHonda extends Bikes{

public void engine() {
System.out.println(“Bikes have Engine”);
}

public void wheels() {
System.out.println(“Bikes have Wheels”);
}

public static void main (String [] args){
HeroHonda abc = new HeroHonda();

abc.seat();
abc.engine();
abc.wheels();
abc.handle();
}
}

Java Interfaces

•  Interface is a Java-type definition block that is 100% abstract.

1. Class vs. Abstract Class

Java Classes have 100% concrete Methods

Abstract Classes have one or more/all abstract methods.

2. Class vs. Interface

Java Classes have 100% concrete Methods

Java Interfaces have 100% Abstract Methods

3 Abstract Class vs. Interface

Abstract Classes have one or more/all abstract methods.

Java Interfaces have 100% Abstract Methods

•  All Interface Methods by default public and abstract.
•  static and final modifiers are not allowed for Interface methods
•  In Interfaces Variables have to initialize at the time of declaration only

Ex:

int a;//Incorrect
a=100;

int b=200;//Correct

• In Interfaces Variables are public and final by default.
• Interfaces are going to be used using the “implements” keyword.

Create Java Interface

Java Project
Java Package
Java Class / Java Interface

Java Interface Example:

public interface Interface1 {

public void engine();
public void seat();
public void wheels();
public void handle();
}

Reuse Methods from Interface to Class

public class ClassNew implements Interface1 {

public void engine() {
System.out.println(“Bikes have Engine”);
}

public void seat() {
System.out.println(“Bikes have Seat”);
}

public void wheels() {
System.out.println(“Bikes have Wheels”);
}
public void handle() {
System.out.println(“Bikes have Handle”);
}
public static void main (String [] args){
ClassNew obj = new ClassNew();
obj.seat();
obj.wheels();
obj.handle();
}
}

Note:

• Reuse Methods from a Class to another Class – using “extends” keyword.
• Reuse Methods from an Abstract Class to Class – using the “extends” keyword.
• Reuse Methods from an Interface to Class – using the “implements” keyword.


Software Testing Tutorials

Manual Testing Tutorial
Manual Testing Video Tutorial
Java Tutorial
Python Tutorial
SQL Tutorial
Selenium, Java, and Testing Videos
Follow me on social media:

Leave a Comment