OVERLOADING AND OVERRIDINGMichael Heron

Introduction• One of the more powerful features for code readability

and usability is that of overloading.• Like most things, it can be used for both good and evil.

• In this lecture, we are going to look at one particular flavour of overloading.• Method overloading.

• In the next lecture we will look at a particulary C++ feature.• Operator overloading.

• Here be dragons

Methods in C++• A method in C++ is not uniquely identified by its name

alone.• Each method has a method signature, consisting of two

elements.• The name of the method• The order and type of its parameters.

• Together, these act as the unique identifier for a C++ method.

• The following thus are two different methods:• addTwo (int x, int y);• addTwo (float x, float y);

Method Overloading• The process of providing more than one method with the

same name is called method overloading.• We say that these methods have been overloaded.

• Overloading makes sure that we can provide a consistent and clear interface to our methods regardless of the parameters type.• We don’t need addTwoInts and addTwoFloats, for example.

Method Overloading• We have already seen this a little bit in constructors.

• It is very good practise to overload constructors give all sensible ways in which an object can be instantiated.

• It is not a feature unique to constructors.• Any method can be overloaded.

• There are only two requirements.• The parameter lists must be unique for each overloaded method

• This means unique as in the order and type of the parameters. Identifiers do not count for this.

• The return type must be the same for all overloaded functions.

• These rules are just as true for Java as they are for C++.

Method Overloading• The compiler works out which of the methods to call

based on the parameters it is passed.• It will check for the method that has a matching signature.• It will execute that method only.

• If no matching signatures are found, a compile-time error will be displayed.• Often with a less than transparent message!

Method Overloadingint add_nums (int one, int two) { return one + two;}

int add_nums (float one, float two) { return (ceil (one + two));}

int main() { int answer_one, answer_two, answer_three;

answer_one = add_nums (1, 2); // Fine answer_two = add_nums (1.0f, 2.0f); // Fine answer_three = add_nums (1.0f, 2) // Error}

Overriding• Overloading is separate and distinct from a related system

called overriding.• This is when