The Basics

Classes, Attributes, & Methods

class example in diagram Figure 1: Class Representation in UML

When you want to represent a class, you display it as a rectangle. This rectangle contains three parts: the name, attributes, and operations. For an example of a class view the figure on the right.

It is common practice to, when writing class names, to exclude spaces and underscores, and to capitalize each word. So, if you wanted to name a class “university student”, the correct format would be “UniversityStudent”. Attributes and operations on the other hand, also exclude spaces and underscores but utilizes camelCase. What this means is that the first word’s starting letter is always lowercase, but the following words’ starting letters should be capitalized. For example, if you were to have an attribute “first name”, you would write it “firstName”. Same with the operation “find book number”, which would be “findBookNumber”.

Attributes also have a type. If you are familiar with coding languages like Java or C++, then you can think of them as the same as variable types. The more common attribute types include:

Attribute Description

string

means that the value contains text (e.g. “Bill”, “5 days”)

char

means that the value is one character long (e.g. ‘i’, 1)

int

means that the value is a number excluding decimals

float

means that the value is a number that includes decimals

bool

means that the value is either “true” or “false”

void

means that there is no value

When identifying an attribute’s type you place it after the attribute name, like this: “firstName:String”. Operations also use types when taking in arguments and when identifying the return object type. The format for putting the operation type is “operationName( int argument1, String argument2 ):String. If you don’t want your operation to return an object, you use the type “void”

Best Practices

When naming your class keep in mind the following guidelines:

  • Name of the class should be a one noun. (i.e. “bankAccount” but not “bankAndAccount”)
  • Name of the class should represent the role it has in the system.
  • Use intuitive names.

When naming your attributes keep in mind the following guidelines:

  • Name of the attribute should be a domain-based noun or a noun phrase or a possessive phrase

When naming your operations keep in mind the following guidelines:

  • Defining operations in the domain class should be avoided.
  • Name of the operation, if defined in the model, should be a verb.