abstract class and its real time usage

Avinash Venkat

7y1.1kLearn iOS Programming

need real time application usage where we use abstract class and its needs

8 Replies

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Ajay Gohil6y ago
A class that is declared using “abstract” keyword is known as abstract class. It can have abstract methods(methods without body) as well as concrete methods (regular methods with body). A normal class(non-abstract class) cannot have abstract methods. In this guide we will learn what is a abstract class, why we use it and what are the rules that we must remember while working with it in Java.
Why we need an abstract class?
Lets say we have a class Animal that has a method sound() and the subclasses of it like Dog, Lion, Horse, Cat etc. Since the animal sound differs from one animal to another, there is no point to implement this method in parent class. This is because every child class must override this method to give its own implementation details, like Lion class will say “Roar” in this method and Dog class will say “Woof”.
So when we know that all the animal child classes will and should override this method, then there is no point to implement this method in parent class. Thus, making this method abstract would be the good choice as by making this method abstract we force all the sub classes to implement this method( otherwise you will get compilation error), also we need not to give any implementation to this method in parent class.
abstract class Animal{
   //abstract method
   public abstract void sound();
}
//Dog class extends Animal class
public class Dog extends Animal{

   public void sound(){
    System.out.println("Woof");
   }
   public static void main(String args[]){
    Animal obj = new Dog();
    obj.sound();
   }
}
output:
Woof
0
Samir Bhogayta6y ago
Please go through this link

https://www.codeproject.com/Tips/888455/When-to-Use-Abstract-Class-in-Csharp-Real-World-Ex
0
Mageshwaran R6y ago
Hi,
Please refer the below link, it might helps you
https://stackoverflow.com/questions/18944539/abstract-class-real-time-example
0
Jayanth Reddy7y ago
Also if a class consists of only the abstract methods it is known as pure abstract class and if it contains both the abstract methods and defined methods then it is known as impure abstract class.
The best example for pure abstract class is "Interface" as it contains only the abstract methods(This can be how we differentiate interface at best).
If we need only code reusabality we can go for simple inheritance( means simply extending a class).The best part of using abstract class when compared to simple inheritance is we can elemenate some n lines of code by extending abstract class as abstract method
doesnt have a definition(Instead of defining in the parent class and re-defining in the child class if we make use of abstract parent class we can define only once i.e,in child class)."So the word REUSING CODE is for inheritance and SAVING CODE is for abstract class.
Also if we make use of interface we have to implement all the methods ,but here in abstract class we have an option to use some selected methods.(Only Abstract methods should be defined for sure)
0
Rajanikant Hawaldar7y ago
Hi Avinash Venkat,

In simple term abstract class concept is moving comman stuff to one class from multiple class, as i understand abstracting is what functionality is needed to showcase(methods, properties) and where to showcase(parent class), Acess spacifier also part of abstraction, encapsulation. Directly or indirectly we also achieved code reusability here by abstracting code. which class can be used as parent class with abstract keyword, a normal class can also be used as parent class but class declared with anstract provide way to have both methods with body and without body( so that according to child class we can change or give implemetation for methods which dont have implemention at parent class) and abstract class does not allow to create object because of having method without implemetation, if allow to create object will be exception when you try to access method whiech don't have implementation.

Go through below thread where you can understand in simple ways

https://www.codeproject.com/Questions/43970/Real-world-examples-of-abstract-classes-and-interf

Thanks
0
Sonu Gupta7y ago
Hi,

Go trough to this URL -
https://www.c-sharpcorner.com/article/when-to-use-abstract-class-and-interface-in-real-time-projects/

Or watch the this video -
https://www.youtube.com/watch?v=yyU3bXyc_oU
+2
Vishal Patel7y ago
Here, Something about abstract class...
An abstract class is an incomplete class so we can't instantiate it.
If methods are abstract, the class must be abstract.
In abstract class, we use abstract and concrete method both.
It is illegal to define a class abstract and final both.
Real-time example--
If you want to make a new car(WagonX) in which all the another car's properties are included like color, size, engine etc.and you want to add some another feature like a model,baseEngine in your car. Then simply you create an abstract class WagonX where you use all the predefined functionality as abstract and another functionality are concrete, which it is defined by you.
Another subclass which extends the abstract class WagonX, By default, it also access the abstract methods which are instantiated in the abstract class.SubClasses also access the concrete methods by creating the subclass's object.

For reusability the code, the developers use abstract class mostly.
abstract class WagonX
{
public abstract void model();
public abstract void color();
public static void baseEngine()
{
// your logic here
}
public static void size()
{
// logic here
}
}
class Car extends WagonX
{
public void model()
{
// logic here
}
public void color()
{
// logic here
}
}
+2
Aakash Maurya7y ago
Copied from here https://stackoverflow.com/a/18944607

A business example:

I have a persistance engine that will work against any data sourcer (XML, ASCII (delimited and fixed-length), various JDBC sources (Oracle, SQL, ODBC, etc.) I created a base, abstract class to provide common functionality in this persistance, but instantiate the appropriate "Port" (subclass) when persisting my objects. (This makes development of new "Ports" much easier, since most of the work is done in the superclasses; especially the various JDBC ones; since I not only do persistance but other things [like table generation], I have to provide the various differences for each database.) The best business examples of Interfaces are the Collections. I can work with a java.util.List without caring how it is implemented; having the List as an abstract class does not make sense because there are fundamental differences in how anArrayList works as opposed to a LinkedList. Likewise, Map and Set. And if I am just working with a group of objects and don't care if it's a List, Map, or Set, I can just use the Collection interface.
+2

abstract class and its real time usage

Why we need an abstract class?