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.

Answer 1

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.

Answer 2

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

class AlertDialog {

   static class Builder {
..