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Abstract Class in Java
Abstract Class in Java
In the world of Java programming, abstract classes play an important role in defining the structure of classes and their behavior in the hierarchy. They provide a blueprint for other teams to follow, and some methods remain undefined. This flexibility empowers developers to generate a well-organized and scalable codebase. In this section, we will explore the concept of abstract classes in Java, examining their features, advantages, and best practices.
A class that is declared with the abstract keyword is known as an abstract class in Java. It can have abstract and non-abstract methods (method with the body).
Before learning the Java abstract class, let's understand the abstraction in Java first.
Abstraction in Java
Abstraction in Java
Abstraction is a process of hiding the implementation details and showing only functionality to the user.
Another way, it shows only essential things to the user and hides the internal details, for example, sending SMS where we type the text and send the message. We do not know the internal processing about the message delivery.
Abstraction lets you focus on what the object does instead of how it does it.
Ways to achieve Abstraction
Ways to achieve Abstraction
There are two ways to achieve abstraction in Java:
Using Abstract Class (0 to 100%)
Using Interface (100%)
Abstract Class in Java
Abstract Class in Java
An abstract class in Java acts as a partially implemented class that itself cannot be instantiated. It exists only for subclassing purposes, and provides a template for its subcategories to follow. Abstract classes can have implementations with abstract methods. Abstract methods are declared to have no body, leaving their implementation to subclasses.
Points to Remember
Points to Remember
An abstract class must be declared with an abstract keyword.
It can have abstract and non-abstract methods.
It cannot be instantiated.
It can have constructors and static methods also.
It can have final methods which will force the subclass not to change the body of the method.
Syntax of Abstract Classes
Syntax of Abstract Classes
In Java, abstract classes are defined using the abstract keyword. Here's a basic syntax example:
public abstract class Shape {
// Abstract method
public abstract double area();
// Concrete method
public void display() {
System.out.println("This is a shape.");
}
}
In this example, Shape is an abstract class with one abstract method area() and one concrete method display(). Subclasses of Shape must implement the area() method, but they can inherit the display() method.
Abstract Method in Java
Abstract Method in Java
A method which is declared as abstract and does not have implementation is known as an abstract method.
Example of abstract method
abstract void printStatus();//no method body and abstract
Example of Abstract Class that has an Abstract Method
Example of Abstract Class that has an Abstract Method
In this example, Bike is an abstract class that contains only one abstract method run. Its implementation is provided by the Honda class.
File Name: Honda4.java
abstract class Bike{
abstract void run();
}
class Honda4 extends Bike{
void run(){System.out.println("running safely");}
public static void main(String args[]){
Bike obj = new Honda4();
obj.run();
}
}
Final Keyword In Java
Final Keyword In Java
The final keyword in java is used to restrict the user. The java final keyword can be used in many context. Final can be:
variable
method
class
The final keyword can be applied with the variables, a final variable that have no value it is called blank final variable or uninitialized final variable. It can be initialized in the constructor only. The blank final variable can be static also which will be initialized in the static block only. We will have detailed learning of these. Let's first learn the basics of final keyword.
Java final variable
Java final variable
If you make any variable as final, you cannot change the value of final variable(It will be constant).
Example of final variable
Example of final variable
There is a final variable speedlimit, we are going to change the value of this variable, but It can't be changed because final variable once assigned a value can never be changed.
class Bike9{
final int speedlimit=90;//final variable
void run(){
speedlimit=400;
}
public static void main(String args[]){
Bike9 obj=new Bike9();
obj.run();
}
}//end of class
Test it Now
Output:Compile Time Error
2) Java final method
2) Java final method
If you make any method as final, you cannot override it.
Example of final method
Example of final method
class Bike{
final void run(){System.out.println("running");}
}
class Honda extends Bike{
void run(){System.out.println("running safely with 100kmph");}
public static void main(String args[]){
Honda honda= new Honda();
honda.run();
}
}
3) Java final class
3) Java final class
If you make any class as final, you cannot extend it.
Example of final class
Example of final class
final class Bike{}
class Honda1 extends Bike{
void run(){System.out.println("running safely with 100kmph");}
public static void main(String args[]){
Honda1 honda= new Honda1();
honda.run();
}
}
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