UML: Creating Class Diagrams

Prerequisites

To use this tutorial, the IDE must be installed on your system and you should be familiar with the basic parts of the IDE. You should also have a basic familiarity with the Java programming language and UML. For a basic understanding of the IDE, see the IDE Basics topics in the online help. A good resource for UML techniques and theory is the official UML resource page at http://www.uml.org/.

Software Needed for This Tutorial

Before you begin, download and install the following software:

• NetBeans IDE 6.0
  
  Select the All Download option.

To Create the Class Diagram

1. If necessary, start the IDE and open the previously created UMLTutorialProject project.
2. In the Projects window, expand the UMLTutorialProject node and right-click the Model node.
3. Choose Add > Diagram from the pop-up menu.
   
   The New Wizard opens and displays the Create New Diagram page.
4. In the Diagram Type list, select Class Diagram.
5. In the Diagram Name field, type ClassDiagram.
6. Leave the default setting in the Namespace field and click Finish.
   The IDE does the following:
   
   • Creates the ClassDiagram node under the Model node
   • Displays the new diagram in the Diagram editor (the diagram is empty at this point)
   • Opens the Modeling Palette

top

To Add and Label Class Elements

1. From the Basic section of the Modeling Palette, select the Class icon and click once in the Diagram editor.
   This action places a Class element on the diagram.
2. Deselect the icon by right-clicking anywhere in the Diagram Editor.
   
   Note: Each time that you select an icon, you can place multiple instances of that element in the Diagram editor by clicking more than once.
3. If not already selected, select the newly added Class element by clicking it once.
4. Type EntryStation and press Enter.
   The IDE does the following:
   
   • Labels the Class element with the name EntryStation
   • Creates a public operation named EntryStation()
   • Displays the Class properties in the Properties window
   • Adds a Class element with the name EntryStation under the Model node in the Projects window

top

To Add Attributes Using the Pop-Up Menu

Now that you have drawn and labeled the EntryStation element, you need to describe its attributes.

1. If it is not already selected, select the EntryStation element in the Diagram editor.
2. Right-click the word Attributes and choose Insert Attribute from the pop-up menu.
   A one-line editor opens and displays the following information:
   

   visibility type name[ranges]=initialValue{name=value}
   

3. Type stationID and press Enter.
   An attribute named stationID of type int appears on the EntryStation class, and the following operations are created on the class:
   

   public int getStationID()
   public void setStationID(int val)
   

   Note that the get and set operations are created because you kept the default setting.

top

To Add Operations

1. In the Diagram editor, Select the EntryStation Class element.
2. Right-click the word Operations and choose Insert Operation from the pop-up menu.
   A one-line editor opens and displays the following information:
   

   visibility returnType name(parameter) {properties, ...}
   

3. Type validateEntryStation and press Enter.
   The IDE creates a new operation.

top

(Optional) To Edit Attributes or Operations

When you double-click an attribute or an operation in a class, a combo box editor opens as shown in the following figure.

As you click each part of the attribute or operation, the label for that part appears in bold type in the combo box. If applicable, the selected part of the operation or attribute has a drop-down list of values.

For example:

1. Double-click the stationID attribute in the EntryStation class.
2. Click the word private.
   Notice that the word visibility appears in bold type.
3. Press CTRL + down arrow.
   A drop-down list opens that displays values that you can select for the visibility attribute.
4. Select a new value from the drop-down list and press Enter.
   The attribute is updated with the new value.
   
   Note: You can also type a new value directly in the editor. If you do not see what you need in the drop-down list, use the right and left arrow keys to position your cursor and type the appropriate value.
5. For this tutorial, use the value private and press Enter to close the editor.

top

To Add and Define the Remaining Classes

Now you need to add more classes to complete a simple banking application Class diagram. After you add the classes, label them and add attributes and operations as described below using the techniques that you have learned so far in this tutorial.

1. From the Basic section of the Modeling Palette, select the Class icon and click five times in the Diagram editor to place the additional class elements as shown in the following figure.
   

   

2. Deselect the Class icon by right-clicking anywhere in Diagram editor.
   
   Note: You can select and drag the new class elements to arrange them as shown in the preceding diagram, so that you can see each one clearly in the diagram.
3. Select the first unnamed Class element below the EntryStation element and name it ATM.
4. With the ATM Class element still selected, add an attribute as follows:
   

   private float cashOnHand

5. Add a second attribute to the ATM class and define it as follows:
   

   private float dispensed
     

   The attributes appear in the Class diagram.
   
   Note: As you add attributes and operations to the classes, the size of the Class elements increases. To improve the appearance of the diagram, move the Class elements as needed so that you can see each element clearly. When doing this, be careful to select the Class element and not an individual attribute or operation.
6. Select the first Class element located below the ATM class and name it Consortium.
7. Add an operation to the Consortium class. Adding operations is similar to adding attributes. Right-click on the word Operations and select Insert Operations.
8. Type validateAccountInfo and press Enter.
   The IDE creates the new operation as follows:
   

   public void validateAccountInfo()
   

9. Select the Class element to the right of the ATM class and label it CashierStation.
10. Add two operations for this class as follows:
    

    public int verifyCard()
    
    public float verifyAmountAvailable()
      

11. Label the two remaining Class elements Branch and User.
    For the User class there are no attributes or operations.
12. For the Branch class, add an attribute as follows:
    

    private char connected
      

To Locate Objects in the Diagram Editor From the Projects Window

• In the Projects window, double-click the EntryStation node.
  In the Diagram editor, the EntryStation Class element is selected and centered.

To Locate Objects in the Projects Window From the Diagram Editor

1. In the Diagram editor, select the Consortium class and right-click it.
2. Choose Select in Model from the pop-up menu.
   In the Projects window, the name of the target object is highlighted.

top

To Use the UML Documentation Window

1. (Optional) If the UML Documentation window is not visible, choose Windows > Other > UML Documentation.
2. In the Diagram editor, select the EntryStation class element.
3. Click inside the UML Documentation window text box.
4. Type Describes the actions of the EntryStation class.
5. Right-click the EntryStation class element and select Generate Code from the pop-up menu.
6. In the Generate Code dialog box, click OK.
7. In the Authorize UML Project Save dialog box, click Yes.
   The new Java code is generated.
8. Click the EntryStation.java Source Editor tab.
   You see that the text you typed in Documentation window has been added to the EntryStation.java source file.

top

To Document Attributes Using the Properties Window

1. Click the ClassDiagram tab to return the focus to the Diagram editor.
2. In the Projects window, expand the EntryStation node.
3. Select the attribute node labeled private boolean isOperating.
   The properties for the attribute appear in the UML Properties window.
4. In the Properties window, click the ellipsis button (...) on the Documentation row.
   A custom editor opens as shown in the following figure.
   

   

5. Type the text Maintains if EntryStation is operating and click OK.
6. In the Diagram editor, right-click the EntryStation class element and select Generate Code from the pop-up menu.
7. In the Generate Code dialog box, click OK.
8. In the Authorize UML Project Save dialog box, click Yes.
   The new Java code is generated.
9. Click the Source Editor tab for EntryStation.java.
   You see the typed text in the source code right above the isOperating attribute.

top

To Document Diagrams Using the Comment Icon

You can add notes that describe specific information for a selected element in the diagram by using the Comment icon located on the Modeling Palette.

1. Click the ClassDiagram tab to return to the Diagram editor.
2. From the Comments section of the Modeling Palette, select the Comment icon .
3. Click once to the right and just above the CashierStation element.
   A Comment element is placed on the diagram.
4. Deselect the icon by right-clicking anywhere in the Diagram editor.
5. While the comment element is selected, type Cashier stations have limited funds and press Enter.
   The text appears in the Comment element.
6. From the Comments section of the Modeling Palette, select the Link Comment icon .
7. Click once inside CashierStation and click again inside the Comment element.
   A link snaps into place between the Comment element and the Class element.
8. Deselect the icon by right-clicking anywhere in the Diagram editor.
9. Repeat steps 2-8 to place and link a second Comment element on the diagram for the Branch Class element.
   Use the following text: A branch belongs to a Member Institution.

To Depict a Class Association

1. From the Association section of the Modeling Palette, select the Aggregation icon .
2. Click inside the ATM element, and then click the Consortium element.
   A link is drawn between the two classes.
3. Right-click anywhere in the Diagram editor to deselect the icon.
   This relationship is represented in the Projects window as shown in the following figure.
   

   

4. Select the Aggregation link between ATM and Consortium.
   When the link is selected, the color changes to blue.
5. Point the cursor near the middle of the selected line and right-click.
6. Choose Labels > Link Name from the pop-up menu.
7. Type AccountVerification in the Name field and press Enter.
   The link is labeled as shown in the following figure.
   

   

8. From the Association section of the Modeling Palette, select the Association icon and draw a link from CashierStation to Branch.
9. Right-click anywhere in the Diagram editor to deselect the icon.

top

To Depict a Qualified Association

A qualified association relates two classes and a qualifier. The qualifier is a special attribute that reduces the effective multiplicity of an association. You depict a qualified association as a small box on the end of the association line near the class it qualifies.

The next step shows you how to create a qualified association between the ATM class and the Consortium class.

• Right-click the Aggregation link where it joins the Consortium class and choose Show Qualifier. A qualifier attaches to the Consortium class element as shown in the following figure.
  

  

top

To Set Multiplicity for the Association

You want to set the multiplicity for this association. However, by default, these labels are hidden. Use the following steps to display the labels on the association link.

1. Right-click the link between Consortium and ATM and choose Labels > Both End Multiplicities.
   The pop-up menu closes and the labels for the link appear.
2. Right-click the small diamond at the upper portion of the aggregation link (near the ATM element) and choose Set Multiplicity.
   
   Note: If you have difficulty making the correct pop-up menu appear, lengthen the aggregate arrow by moving the Consortium element farther away from the ATM element.
3. Select 1..*.
   Notice that the lower portion of the link is labeled 1 as shown in the following figure.
   

   

4. Follow a similar procedure and set the multiplicity for the Association link between CashierStation and Branch as shown in the following figure.

   

top

To Depict Generalization and Inheritance

Generalization is the relationship between a class and one or more refined versions of this class. The class being refined is named the superclass and each refined version is named the subclass. The attributes and operations of the superclass can be exhibited in its subclasses, as a result, each subclass is said to inherit the features of the superclass. You can organize classes by using inheritance to share common structure. A generalization link means that a class can inherit an array of attributes and operations from the parent class.

1. From the Basic section of the Modeling Palette, select the Generalization icon .
2. Click inside the ATM class element, and then click the EntryStation class element.
   The Select Methods to Redefine dialog box appears.
3. Select the checkbox next to the ATM node to select all the methods and click OK.
   The selected methods are added to the ATM class element and a generalization link snaps in place between the two class elements.
4. Draw another generalization link by first clicking CashierStation, and then clicking EntryStation.
5. In the Select methods to Redefine dialog box, select the checkbox next to the CashierStation node to select all methods and click OK.
6. Right-click anywhere in the Diagram editor to deselect the Generalization icon.
7. Your finished diagram should look similar to the following figure.