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Class Diagram in IntelliJ IDEA 8

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Class Diagram in IntelliJ IDEA 8

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IntelliJ IDEA 8 is already here. It is so feature-rich that it’s rather hard to tell what is most important – improved testing support, or new refactorings, injected languages, or handy interaction with data sources. In due time, we’ll dig deeper into all the new features.

Let’s begin with something brand-new for IntelliJ IDEA, namely UML Class diagram support. This feature is actually the first attempt to approach UML modeling, and thus requires further finishing and fine-tuning. Try Class diagram with IDEA hands-on – your feedback will be appreciated and considered in further revisions.

You can use UML Class diagram for two purposes:

  • To create a visual model, populate it with node elements and members, and have the underlying code generated automatically (forward engineering).
  • To explore existing source code, understand its hierarchy and dependencies (reverse engineering).

Creating visual model

To demonstrate visual modeling with IntelliJ IDEA UML Class diagram in action, we’ll create a new Java project, add a package (for example, animals), and press (take care of your fingers) Ctrl+Alt+Shift+U. Context menu of the diagram helps create all the required elements, but, since IntelliJ IDEA is strongly keyboard-centric, we’ll use keyboard shortcuts.







Press Shift+C to create new classes, for example, Animals, and Carnivore. Now press Shift+I to create an interface, say, Huntable. Note a very handy way to add node elements to a diagram: select a class in the Project view and just drag it to the diagram background:









Next step is to add fields and methods to node elements. Here, again, you can use context menu commands, or keyboard shortcuts. For example, having selected a node element, press Shift+M, and define method name, type and parameters, if any:








Now, let’s create relationship links between node elements. For this purpose, you have to enable the special edge drawing mode by clicking edge drawing mode button [img_assist|nid=5884|title=|desc=|link=none|align=undefined|width=26|height=23] on the diagram toolbar. IntelliJ IDEA can smartly tell the type of relationship link, depending on the source and target nodes.

Suppose you draw a link from a class to an interface:









Click the Generate methods button, and select the methods you want to be implemented.

Look into the source code of the Carnivore class, and see that implements clause has been generated, together with the selected methods’ stubs. Drawing a link between two classes, results in generating extends clause:











Exploring code base with UML Class diagram

Let’s see how you can use Class diagram in IntelliJ IDEA to reverse engineer source code, and view its structure, hierarchies and dependencies. Select a library package, for example, java.beans, and open its Class diagram:








What does IntelliJ IDEA suggest to get as much information as possible? Actually, all facilities are on the diagram toolbar and context menu… however, as it is custom for IntelliJ IDEA, you can do everything using both the keyboard, and pointing device.

If a diagram is too large, get a “10,000-feet view” of it in the Structure tool window. To do that, just press Alt+7:







The gray rectangle represents the currently visible area of the diagram. Dragging this rectangle reveals the corresponding portion of diagram. You can zoom in and out using the NumPad plus and minus keys, or rotate your mouse wheel.

If the names of the node elements are long, you can reduce them to the capital letters only by pressing Alt+N. Pointing to a node shows its fully qualified name at the tooltip:










If we want to see the node elements with their members, rather than just class names in the title bars, press the toolbar buttons [img_assist|nid=5903|title=|desc=|link=none|align=left|width=98|height=25]

, or use keyboard shortcuts to show fields (Alt+F), constructors (Alt+C), methods (Alt+M) and inner classes (Alt+I) respectively:













To show the package the selected node belongs to, just press C, and the diagram will collapse to the container package:







The opposite action (E) expands selected package and shows its Class diagram. You can also easily visualize the nodes that reside in the same package, or in subpackages. To do that, select a node element in diagram, and press Space bar. The sibling nodes are highlighted yellow, and the nodes that belong to subpackages of the current package are green. The nodes that reside outside of the current package are not highlighted:










If you point to a package, a tooltip appears with the complete information about the package - its name, number of contained classes and subpackages.

Suppose that you want to explore only a portion of diagram, and remove from view those elements that are of no interest for you. In this case, use the Delete key. The node elements are deleted from diagram, but the corresponding files are left intact. (If you want to physically delete an element, use Safe Delete refactoring).

For exploring dependencies, click the show dependencies button [img_assist|nid=5902|title=|desc=|link=none|align=left|width=25|height=23] on the diagram toolbar

. As you select a node element, its dependency links appear in diagram:









Needless to say that handy navigation shortcuts, search for usages, analysis of dependencies and refactorings you are used to in IntelliJ IDEA, are available in Class diagram too.

Try the live demo at



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