Reverse Engineering: Creating UML diagrams with existing code

Very often it happens that whenever a new person joins the project the seniors gave him/her the design documents of the project and in most of the cases they tell “Hey there has been lot of changes in the original design and the class and sequence diagram that you see in this document is obsolete” and the poor chap has go through the arduous task of going through the source code to understand the design. This is a common problem in every project and but fortunately the reverse engineering feature of Netbeans comes to our rescue using which we can create UML diagrams of an existing code. Let’s look at a small example

I had defined an abstract class Person

abstract public class Person
{
    protected String name;
    protected boolean haveBrain;

    Person(String name)
    {
        this.name = name;
    }
   protected abstract void display();
}

There are 2 classes SoftwareEngineer and Farmer which extends the class Person

public class SoftwareEngg extends Person
{
    SoftwareEngg(String name)
    {
        super(name);
        haveBrain = false;
    }

    @Override
    protected void display()
    {
        System.out.println("Hi dude I am a Software engineer");
        System.out.println("Name: " + name);
        System.out.println("Do I have brain? " + haveBrain);
    }
}

public class Farmer extends Person
{
    Farmer(String name)
    {
        super(name);
        haveBrain = true;
    }
    @Override
    protected void display()
    {
        System.out.println("Ram ram bhaiya!");
        System.out.println("Name: " + name);
        System.out.println("Do I have brain? " + haveBrain);
    }
}

Also I had created a Factory class that returns an object of Person

public class PersonFactory
{
    public static Person getPerson(int ch, String name)
    {
        switch(ch)
        {
            case 1: return new SoftwareEngg(name);
            case 2: return new Farmer(name);
        }
        return new Farmer(name);
    }
}

Finally there is a class called PersonImpl that has the main method

public class PersonImpl
{
    public static void main(String[] args)
    {
        Person per = PersonFactory.getPerson(1, "TheDude");
        per.display();
        per = PersonFactory.getPerson(2, "Ramlal");
        per.display();
    }
}

Steps for generating UML diagrams

1. I am using Netbeans 6.5. Go to Tools --> Plugins and in the Available plug-ins search for “uml” and install the UML package and restart the IDE.

2. Once the IDE restarts right click on the Project node (in the Project navigation tree) and select “Reverse Engineer” option. A new node -Model will be created and you will see something like this in output/log window

Begin processing Reverse Engineering


Parsing 5 elements

Analyzing attributes & operations for 5 symbols

Resolving 5 attribute types

Integrating 5 elements

Building the query cache.

================================
Task Successful (total time: 2 seconds)


3. Now the project navigator looks something like this




4. Now right click on sub node reverseengg (“reverseengg” is the package name of my original project) and select “Create Diagram From Selected Elements…”, a new dialog will pop up and you can select any diagram. For this case I will select Class diagram and boom! we get a nice class diagram showing the relation between various classes