Abstract Classes
An abstract class is an unfinished blueprint you cannot build directly. It sets rules and leaves some parts for the classes that inherit from it to fill in.
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Syntax
abstract class ClassName
{
public abstract ReturnType MethodName(); // no body
}
class DerivedClass : ClassName
{
public override ReturnType MethodName() { }
}Abstract Classes
An abstract class cannot be instantiated directly and may declare abstract methods that have no body — derived classes are *required* to implement them.
Abstract classes model a shared concept that only makes sense through its concrete subtypes, like Shape without a specific area formula. They can still contain regular, fully-implemented methods alongside abstract ones.
Warning:
Trying to write
new Shape() on an abstract Shape class is a compile error.Example: Abstract Classes
using System;
abstract class Shape
{
public abstract double Area();
public void Describe()
{
Console.WriteLine($"Area is {Area()}");
}
}
class Square : Shape
{
public double Side;
public Square(double side)
{
Side = side;
}
public override double Area()
{
return Side * Side;
}
}
class Program
{
static void Main(string[] args)
{
Square sq = new Square(4);
sq.Describe();
}
}Login to try C/C++/Java/PHP code in the editor
Related Topics
{# common_mistakes/chapter_summary/browser_support: on Hindi pages the
view already swaps in the hi_ translation fields (or blanks these
out if untranslated), so this renders correctly for both languages
without a lang_code check here. #}
Common Mistakes
- Trying to create an object of an abstract class with
new, which is a compile error. - Not implementing every abstract member in the derived class, which is a compile error unless the class is also abstract.
- Giving an abstract method a body, which is not allowed.
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