Before you keep reading...

Runestone Academy can only continue if we get support from individuals like you. As a student you are well aware of the high cost of textbooks. Our mission is to provide great books to you for free, but we ask that you consider a $10 donation, more if you can or less if $10 is a burden.

Support Runestone Academy Today

Before you keep reading...

Making great stuff takes time and $$. If you appreciate the book you are reading now and want to keep quality materials free for other students please consider a donation to Runestone Academy. We ask that you consider a $10 donation, but if you can give more thats great, if $10 is too much for your budget we would be happy with whatever you can afford as a show of support.

Support Runestone Academy Today

20.5. Class Diagrams

The two major types of relationships between classes are association and inheritance. The Unified Modeling Language (UML) is a graphical notation that provides a standard for depicting classes and the relationships between them. It gives software engineers a way to record both their proposed designs, as well as the design of the final product. Put another way, UML provides the notation for constructing blueprints for software, and since it is widely used in both industry and academia, it is important for you to have some familiarity with it.

UML defines notations for several different kinds of diagrams. Here, we will introduce class diagrams, one of the most common UML diagrams. Class diagrams can contain a number of different elements, but we will focus on the basics: showing classes with their instance variables and methods, and the relationships between classes.

On a UML class diagram, a class is depicted as a rectangle with three sections. The top section contains the class name; the middle section, the instance variables (attributes); and the bottom section, the methods (behaviors). The following diagram shows the classes Point and LabeledPoint in an inheritance relationship where LabeledPoint is a child (subclass) of Point.

Q-1: Which of the following are attributes of the LabeledPoint class as shown above. Select all that apply.

• x
• LabeledPoint inherits this attribute from Point.
• y
• LabeledPoint inherits this attribute from Point.
• label
• This is an attribute of a LabeledPoint object.
• distanceFromOrigin
• LabeledPoint inherits this method (behavior) from Point.

The class diagram below shows an association relationship between Point and LabeledPoint.

Q-2: Which of the following are attributes of the LabeledPoint class as shown above. Select all that apply.

• x
• This is an attribute of Point.
• y
• This is an attribute of Point.
• label
• This is an attribute of a LabeledPoint object.
• point
• This is an attribute of a LabeledPoint object.

Q-3: Drag each item to its location in a class diagram Read the chapter on functions and try again.
• methods
• in the bottom section of a class diagram
• attributes
• in the middle section of a class diagram
• class name
• in the top section of a class diagram

You have attempted of activities on this page