What is the dot-notation between class names and what does it mean?

Question

What is the meaning of this .notation (AlertDialog.Builder) in a class constructor?

public Dialog onCreateDialog(Bundle savedInstanceState) {

    return new AlertDialog.Builder(getActivity())
        .setTitle(R.string.date_picker_title)
        .setPositiveButton(android.R.string.ok, null)
        .create();

}

Does it mean that the Builder class is defined inside the AlertDialog class? Or Builder is a method, but its first letter is capitalized so I'm confused.

That's [fluent](http://en.wikipedia.org/wiki/Fluent_interface). They just inserted line breaks for clarity. — Tim S., Sep 26 '13 at 14:39
See [here](http://stackoverflow.com/questions/16976150/benefits-and-drawbacks-of-method-chaining-and-a-possibility-to-replace-all-void) for more information on method chaining and remember that whitespace largly has no meaning to the compiler. Imagine it all on one line — Richard Tingle, Sep 26 '13 at 14:41

score 13 · Accepted Answer · answered Sep 26 '13 at 14:36

13

This pattern is called method chaining.

Builder is a static inner class of AlertDialog.

Each method in Builder returns a Builder (usually "this") instead of void.

answered Sep 26 '13 at 14:36

dkatzel

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Evgeniy Dorofeev · Answer 2 · 2013-09-26T15:12:23.387

2

This means that Builder is a static nested class in AlertDialog class, that is

class AlertDialog {

   static class Builder {
..

edited Sep 26 '13 at 15:12

answered Sep 26 '13 at 14:36

Evgeniy Dorofeev

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score 0 · Answer 3 · answered Sep 26 '13 at 14:36

0

Builder is a static inner class of the AlertDialog class.

I advise you to read this about the use and the utility of nested classes

answered Sep 26 '13 at 14:36

Alexis C.

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score 0 · Answer 4 · answered Sep 26 '13 at 14:36

0

Check out the documentation!

Builder is a static class defined within the AlertDialog class. You are calling it's constructor.

answered Sep 26 '13 at 14:36

Bryan Herbst

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Mario Kutlev · Answer 5 · 2013-09-26T15:05:43.240

This is Builder design pattern.

What you do in your code:

Create instance of the Builder class - new AlertDialog.Builder(getActivity())
Set its properties calling setTitle and setPositiveButton
Create instance of AlertDialog by calling create() method with the properties of the Builder.

Builder pattern is a creational design pattern it means it solves problem related to object creation. Constructors in Java are used to create object and can take parameters required to create object. Problem starts when an Object can be created with lot of parameters, some of them may be mandatory and others may be optional. Builder Design pattern should be used when number of parameter required in constructor is more than manageable usually 4 or at most 5.

What is the dot-notation between class names and what does it mean?

5 Answers5