Fonctions : entêtes

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En provenance du cours de École Polytechnique Fédérale de Lausanne

Initiation à la programmation (en Java)

217 notes

École Polytechnique Fédérale de Lausanne

Initiation à la programmation (en Java)

217 notes

Ce cours initie aux bases de la programmation en utilisant le langage Java : variables, boucles, fonctions, ... Il ne présuppose pas de connaissance préalable. Les aspects plus avancés (programmation orientée objet) sont donnés dans un cours suivant, «Introduction à la programmation orientée objet (en Java)». Il s'appuie sur de nombreux éléments pédagogiques : vidéos sous-titrées, quizz dans et hors vidéos, exercices, devoirs notés automatiquement, notes de cours.

À partir de la leçon

Fonctions / Méthodes

Cette semaine aborde un sujet fondamental en programmation : les « fonctions » qui permettent de beaucoup mieux structurer les programmes et d'éviter d'avoir à récrire plusieurs fois la même portion de code.

Fonctions : introduction12:00

Fonctions : appel8:17

Fonctions : passage des arguments16:12

Fonctions : entêtes3:37

Fonctions : définitions16:42

Fonctions : méthodologie5:40

Fonctions : surcharge5:19

Rencontrer les enseignants

Jean-Cédric Chappelier
Dr.
School of Computer and Communication Sciences
Jamila Sam
Dr
School of Computer and Communication Sciences

In a previous episode, we went over

the three aspects of methods.

We also talked about the call (of a method).

Now, we will concentrate

on the concept of "method header".

Consider, for example, the following complete example

where we wanted to compute the mean of two numbers.

The header of the <i>moyenne</i> method is this line here ("moyenne" means "mean").

A method is characterized by a header,

that is, a description of its name;

the set of parameters that the method must receive from the rest

of the program to be able to do the job; and by the type of its return value

which the method will send back to the rest of the program.

The syntax for the declaration of a header is the following:

we start by the return type of the method,

followed by the name we chose for it and, between parentheses,

its set of parameters, which can be empty,

parameters the method must receive from the rest of the program in order to work.

In this lesson, we will also add the <i>static</i> keyword

in front of the header; here, in front of the return type.

This is specific to this introductory course,

but will become an exception

and will be explained in the object-oriented programming course.

Here are a few header examples.

This is the header of the example

mean-calculating method which we went over in the previous slide.

Here we can see the name of the method, <i>moyenne</i>;

the return type, <i>double</i>, preceded by the <i>static</i> keyword here;

and finally, between parentheses, the two parameters

which we pass to the <i>moyenne</i> method

to compute the mean of these two values.

Another example here, with a method which does not take any arguments:

here, we simply give an empty set of parameters to indicate

that the method which draws a random number

does not require any information from the rest of the program to do its job.

Here are now a few tips for good practices

concerning writing method headers.

First, choose relevant names,

names which are descriptive, which tell what the method actually does.

This will make your code clear and easily understandable

and easier to maintain.

But of course, this supposes

that the method will do only what it was designed to do.

It must not have what is called "side effects",

that is, undesirable effects.

For example, if you have a method which calculates the square root of a number,

which would be called "<i>sqrt</i>" and which would take a parameter<i>x</i> of type <i>double</i>,

and which would return the square root of <i>x</i> in the form of a <i>double</i>,

you would not expect

this method to write the value in the terminal,

or to print error messages.

You expect it to do only one thing:

to calculate this value

and to return it to the rest of the program

without polluting the outputs

or doing anything unwanted,

any "side effect".

Finally, last tip,

always start by writing the header of your method

before writing the body of the method.

Think first of the "what", that is, the name,

what the method needs as parameters to work,

and what it needs to return to the rest of the program

before thinking about the "how",

that is, the specifics of the method's body.

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