Java Abstraction
Abstraction is a way to hide details of actual implementation and provide abstract information of class and such class is called abstract class, the class which uses(extends) abstract class is responsible for implementation of logic of abstract class. This is called abstraction concept of OOP in java.
Abstract Class
Abstract class is defined with abstract keyword in class name, few important points related to abstract class in java-
- Abstract class will always have abstract key word with class name.
- Abstract method is just definition or signature of a method but actual implementation is not provided and class which extends it will be responsible for implementation.
- Abstract class may or may not have abstract method.
- Abstract class may or may not have concrete or implemented methods.
- Abstract class can’t be instantiated.
Abstract Method
Abstract methods are defined in an abstract class with abstract keyword.
- Abstract method will always be inside an abstract class.
- Abstract method will have abstract keyword with method name.
- Abstract class and methods can’t be initialized or accessed directly, a sub class should extend it and provide implementation of all abstract methods in abstract class.
Example of Abstract Class, Method and Usage
In below code you can see different abstract classes, Car and Car1 are abstract and there is no implementation class so can’t be used or initialized, Car2 is extended and implemented by ElectricCar class and so abstract method is implemented and also already implemented abstract method is available in ElectricCar.
//Abstract class with nothing
abstract class Car {
}
//Abstract class with one already implemented method
abstract class Car1 {
public void showCarName() {
System.out.println("Car name is car1");
}
}
//Abstract class with abstract and normal methods
abstract class Car2 {
abstract void showCarPrize();
public void showCarName() {
System.out.println("Car name is Ford");
}
}
class ElectricCar extends Car2 {
@Override
void showCarPrize() {
System.out.println("eCar prize is 200000 USD");
}
}
class AbstractDemo {
public static void main(String[] args) {
Car2 eCar = new ElectricCar();
eCar.showCarName();
eCar.showCarPrize();
}
}
Output:
Car name is Ford
eCar prize is 200000 USD
References
Reference article from Oracle:Â Java Abstraction