BlueJ - UML

[Nghi97]

Hey,

I am a newbie in Java programming and started with Java in BlueJ.
There is a UML diagram with arrows.
What is the meaning of these arrows? I removed them, and the program is still working.

How is it when I do not use BlueJ and have 2 different classes.
How do I combine the 2 classes?

[jeroenvanveghel]

Those arrows can mean several things, but in your case i guess it's the following:

When there is a line pointed from class A to class B.

It means class A has a relationship with class B, what relationship this is, depends on what you've set.
In this example the dotted line means: (someone correct me if I'm wrong):
class A makes use of class B, or something what's inside class B

[Nghi97]

Hey,

thank you for your answer.
Is it only for overview purposes? Because it works without the arrows.
If not, how do I let class A makes use of class B in another simple text-editor?

[jeroenvanveghel]

It's been quite a long time since I used BlueJ, though what I recall is that you can safely delete these arrows and that it's only used for overview purposes indeed.
You make classes use eachother inside your code.
for example you have a class named Address.
Inside this class you have some variables:
public String streetName;
public int houseNumber;
public String postalCode;

Now you have another class named Person.
And you want to have some information about that person, for example you want to have it an Address.
You can now do the following inside your Person class, you can declare a variable of the class Address:
private Address personsAddress;

You now make use of the class Address inside your class Person.
My guess is also that BlueJ will now automatically create an arrow in your class diagram.
This will also work in any other IDE for java.

(sorry for the unillustrated/little example, I just hope this is clear enough for you)

[Nghi97]

Yes, I think it was very helpful, thank you :)
So I do not have to import or declare somewhere else, that I want to use the class address?
That fact is new, because I have programmed always in PHP.

[jeroenvanveghel]

That depends if you are in the same package.
If you have classes that exist in different packages (in .Net this is called namespace, for PHP i have no idea ;-) ) you'll have to import it.