Main method and constructor

[dbrb2]

Sorry for the basic question I'm asking - I'm a bit unfamiliar with Java!

I'm getting a bit confused concerning the distinction between the main method and the constructor. Is the difference that the constructor is only called when the class is first created, while the main method is called each time the java application is run ...?

Thanks,

Ben

 

[Custom24]

That's kind of it. The main method for a class is the entry point into the application - not every class needs one - only the class which you launch the app with at the command line.

The constructor for a class is called when each new instance of a class is created in the calling code. If you don't need to do anything in the constructor, you don't need to provide one - Java will create a default one for you, so you can still instantiate the class.

Hope this helps.

Mark

 

[stefanwagner]

... and you normally have lot's of classes, and a lot of instances (objects) per class, so there are hundrets of constructors called, and each maybe multiple times.

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[dbrb2]

Wheras if you have a main class at all, you would only ever have one of them?

Thanks to both of you for your help



Ben

 

[chiph]

Actually, you can put a static main method in every class if you want -- you just need to tell the compiler which one to use.

One use for this is in unit testing -- you can put unit tests in each class' main method, and just call them one at a time. A better solution would be to use JUnit, of course, but I've seen both techniques used.

Chip H.


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[stefanwagner]

and you may call 'main' inside your code, as every other method.
But it's not usual to do so.

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