Question

Why not

AlertDialogBuilder builder = new  AlertDialogBuilder(this);
builder.setTitle("foo");

instead of

AlertDialog.Builder builder = new  AlertDialog.Builder(this);
builder.setTitle("foo");

Update: I want to know the reason behind this kind of writing/organization

Answer 1

Builder is the static inner class inside the AlertDialog class. So to create a Builder class object, you need to call AlertDialog.Builder.

As there is no class like AlertDialogBuilder so you cannot do that.

If you want you can also use as like bellow.

Builder builder = new Builder(this);
builder.setTitle("foo");

But to use like this you need to import the Builder class to your class like

import android.app.AlertDialog.Builder;

instead of just

import android.app.AlertDialog;

A simple example

class A{
     static class B{}
}

you cannot use

AB obj = new AB();

you have to use

A.B obj = new A.B();

Hope you are clear now.