Ada

Ada provides method overriding by default. To favor early error detection (e.g. a misspelling), it is possible to specify when a method is expected to be actually overriding, or not. That will be checked by the compiler.

  type T is new Controlled with ......;
  procedure Op(Obj: in out T; Data: in Integer);

  type NT is new T with null record;
  overriding    -- overriding indicator
  procedure Op(Obj: in out NT; Data: in Integer);
  overriding    -- overriding indicator
  procedure Op(Obj: in out NT; Data: in String);
  -- ^ compiler issues an error: subprogram "Op" is not overriding

C#

C# does support method overriding, but only if explicitly requested using the modifiers overrideCategory:Articles with example C Sharp code and virtualCategory:Articles with example C Sharp code or abstractCategory:Articles with example C Sharp code.

abstract class Animal
{
    public          string Name { get; set; }
    // Methods
    public          void   Drink();
    public virtual  void   Eat();
    public          void   Go();
}

class Cat : Animal
{
    public new      string Name { get; set; }
    // Methods
    public          void   Drink();  // Warning: hides inherited drink(). Use new
    public override void   Eat();    // Overrides inherited eat().
    public new      void   Go();     // Hides inherited go().
}

When overriding one method with another, the signatures of the two methods must be identical (and with same visibility). In C#, class methods, indexers, properties and events can all be overridden.

Non-virtual or static methods cannot be overridden. The overridden base method must be virtual, abstract, or override.

In addition to the modifiers that are used for method overriding, C# allows the hiding of an inherited property or method. This is done using the same signature of a property or method but adding the modifier newCategory:Articles with example C Sharp code in front of it.^[6]

In the above example, hiding causes the following:

Cat cat = new Cat();

cat.Name = …;             // accesses Cat.Name
cat.Eat();                // calls Cat.Eat()
cat.Go();                 // calls Cat.Go()
((Animal)cat).Name = …;   // accesses Animal.Name!
((Animal)cat).Eat();      // calls Cat.Eat()!
((Animal)cat).Go();       // calls Animal.Go()!

C++

C++ does not have the keyword superCategory:Articles with example C++ code that a subclass can use in Java to invoke the superclass version of a method that it wants to override. Instead, the name of the parent or base class is used followed by the scope resolution operator. For example, the following code presents two classes, the base class RectangleCategory:Articles with example C++ code, and the derived class BoxCategory:Articles with example C++ code. BoxCategory:Articles with example C++ code overrides the RectangleCategory:Articles with example C++ code class's PrintCategory:Articles with example C++ code method, so as also to print its height.^[7]

#include <iostream>

//---------------------------------------------------------------------------
class Rectangle {
 public:
  Rectangle(double l, double w) : length_(l), width_(w) {}
  virtual void Print() const;

 private:
  double length_;
  double width_;
};

//---------------------------------------------------------------------------
void Rectangle::Print() const {
  // Print method of base class.
  std::cout << "Length = " << length_ << "; Width = " << width_;
}

//---------------------------------------------------------------------------
class Box : public Rectangle {
 public:
  Box(double l, double w, double h) : Rectangle(l, w), height_(h) {}
  void Print() const override;

 private:
  double height_;
};

//---------------------------------------------------------------------------
// Print method of derived class.
void Box::Print() const {
  // Invoke parent Print method.
  Rectangle::Print();
  std::cout << "; Height = " << height_;
}

The method PrintCategory:Articles with example C++ code in class BoxCategory:Articles with example C++ code, by invoking the parent version of method PrintCategory:Articles with example C++ code, is also able to output the private variables lengthCategory:Articles with example C++ code and widthCategory:Articles with example C++ code of the base class. Otherwise, these variables are inaccessible to BoxCategory:Articles with example C++ code.

The following statements will instantiate objects of type RectangleCategory:Articles with example C++ code and BoxCategory:Articles with example C++ code, and call their respective PrintCategory:Articles with example C++ code methods:

int main(int argc, char** argv) {
  Rectangle rectangle(5.0, 3.0);

  // Outputs: Length = 5.0; Width = 3.0
  rectangle.Print();

  Box box(6.0, 5.0, 4.0);

  // The pointer to the most overridden method in the vtable in on Box::print,
  // but this call does not illustrate overriding.
  box.Print();

  // This call illustrates overriding.
  // outputs: Length = 6.0; Width = 5.0; Height= 4.0
  static_cast<Rectangle&>(box).Print();
}

In C++11, similar to Java, a method that is declared final in the super class cannot be overridden; also, a method can be declared override to make the compiler check that it overrides a method in the base class.

Delphi

In Delphi, method overriding is done with the directive override, but only if a method was marked with the dynamic or virtual directives.

The inherited reserved word must be called when you want to call super-class behavior

type
  TRectangle = class
  private
    FLength: Double;
    FWidth: Double;
  public
    property Length read FLength write FLength;
    property Width read FWidth write FWidth;

    procedure Print; virtual;
  end;

  TBox = class(TRectangle)
  public
    procedure Print; override;
  end;

Eiffel

In Eiffel, feature redefinition is analogous to method overriding in C++ and Java. Redefinition is one of three forms of feature adaptation classified as redeclaration. Redeclaration also covers effecting, in which an implementation is provided for a feature which was deferred (abstract) in the parent class, and undefinition, in which a feature that was effective (concrete) in the parent becomes deferred again in the heir class. When a feature is redefined, the feature name is kept by the heir class, but properties of the feature such as its signature, contract (respecting restrictions for preconditions and postconditions), and/or implementation will be different in the heir. If the original feature in the parent class, called the heir feature's precursor, is effective, then the redefined feature in the heir will be effective. If the precursor is deferred, the feature in the heir will be deferred.^[8]

The intent to redefine a feature, as messageCategory:Articles with example Eiffel code in the example below, must be explicitly declared in the inheritCategory:Articles with example Eiffel code clause of the heir class.

class
    THOUGHT
feature
    message
            -- Display thought message
        do
            print ("I feel like I am diagonally parked in a parallel universe.%N")
        end
end

class
    ADVICE
inherit
    THOUGHT
        redefine
            message
        end
feature
    message
            -- Precursor
        do
            print ("Warning: Dates in calendar are closer than they appear.%N")
        end
end

In class ADVICECategory:Articles with example Eiffel code the feature messageCategory:Articles with example Eiffel code is given an implementation that differs from that of its precursor in class THOUGHTCategory:Articles with example Eiffel code.

Consider a class which uses instances for both THOUGHTCategory:Articles with example Eiffel code and ADVICECategory:Articles with example Eiffel code:

class
    APPLICATION
create
    make
feature 
    make
            -- Run application.
        do
            (create {THOUGHT}).message;
            (create {ADVICE}).message
        end
end

When instantiated, class APPLICATIONCategory:Articles with example Eiffel code produces the following output:

I feel like I am diagonally parked in a parallel universe.
Warning: Dates in calendar are closer than they appear.

Within a redefined feature, access to the feature's precursor can be gained by using the language keyword PrecursorCategory:Articles with example Eiffel code. Assume the implementation of {ADVICE}.messageCategory:Articles with example Eiffel code is altered as follows:

    message
            -- Precursor
        do
            print ("Warning: Dates in calendar are closer than they appear.%N")
            Precursor
        end

Invocation of the feature now includes the execution of {THOUGHT}.messageCategory:Articles with example Eiffel code, and produces the following output:

Warning: Dates in calendar are closer than they appear.
I feel like I am diagonally parked in a parallel universe.

Java

In Java, when a subclass contains a method with the same signature (name and parameter types) as a method in its superclass, then the subclass's method overrides that of the superclass. For example:

class Thought {
    public void message() {
        System.out.println("I feel like I am diagonally parked in a parallel universe.");
    }
}

public class Advice extends Thought {
    @Override  // @Override annotation in Java 5 is optional but helpful.
    public void message() {
        System.out.println("Warning: Dates in calendar are closer than they appear.");
    }
}

Class Thought Category:Articles with example Java code represents the superclass and implements a method call message() Category:Articles with example Java code. The subclass called Advice Category:Articles with example Java code inherits every method that could be in the Thought Category:Articles with example Java code class. Class Advice Category:Articles with example Java code overrides the method message() Category:Articles with example Java code, replacing its functionality from Thought Category:Articles with example Java code.

Thought parking = new Thought();
parking.message();  // Prints "I feel like I am diagonally parked in a parallel universe."

Thought dates = new Advice();  // Polymorphism
dates.message();  // Prints "Warning: Dates in calendar are closer than they appear."

When a subclass contains a method that overrides a method of the superclass, then that (superclass's) overridden method can be explicitly invoked from within a subclass's method by using the keyword super Category:Articles with example Java code.^[3] (It cannot be explicitly invoked from any method belongings to a class that is unrelated to the superclass.) The super Category:Articles with example Java code reference can be

public class Advice extends Thought {
      @Override
      public void message() {
          System.out.println("Warning: Dates in calendar are closer than they appear.");
          super.message();  // Invoke parent's version of method.
      }

There are methods that a subclass cannot override. For example, in Java, a method that is declared final in the super class cannot be overridden. Methods that are declared private or static cannot be overridden either because they are implicitly final. It is also impossible for a class that is declared final to become a super class.^[9]

Kotlin

In Kotlin we can simply override a function like this (note that the function must be open Category:Articles with example Java code):

fun main() {
    val p = Parent(5)
    val c = Child(6)
    p.myFun()
    c.myFun()
}

open class Parent(val a : Int) {
    open fun myFun() = println(a)
}

class Child(val b : Int) : Parent(b) {
    override fun myFun() = println("overrided method")
}

Python

In Python, when a subclass contains a method that overrides a method of the superclass, you can also call the superclass method by calling super(Subclass, self).methodCategory:Articles with example Python (programming language) code^[10] instead of self.methodCategory:Articles with example Python (programming language) code. Example:

class Thought:
    def __init__(self) -> None:
        print("I'm a new object of type Thought!")
    def message(self) -> None:
        print("I feel like I am diagonally parked in a parallel universe.")

class Advice(Thought):
    def __init__(self) -> None:
        super(Advice, self).__init__()
    def message(self) -> None:
        print("Warning: Dates in calendar are closer than they appear")
        super(Advice, self).message()

t = Thought()
# "I'm a new object of type Thought!"
t.message()
# "I feel like I am diagonally parked in a parallel universe.

a = Advice()
# "I'm a new object of type Thought!"
a.message()
# "Warning: Dates in calendar are closer than they appear"
# "I feel like I am diagonally parked in a parallel universe.

# ------------------
# Introspection:

isinstance(t, Thought)
# True

isinstance(a, Advice)
# True

isinstance(a, Thought)
# True

Ruby

In Ruby when a subclass contains a method that overrides a method of the superclass, you can also call the superclass method by calling super in that overridden method. You can use alias if you would like to keep the overridden method available outside of the overriding method as shown with 'super_message' below.

Example:

class Thought
  def message
    puts "I feel like I am diagonally parked in a parallel universe."
  end
end

class Advice < Thought
  alias :super_message :message
  def message
    puts "Warning: Dates in calendar are closer than they appear"
    super
  end
end