Bitrix Framework

The method isFilled is used to verify, if object contains a current actual value from the database:

use \Bitrix\Main\Test\Typography\Book;

// Values from fetch* and wakeUp methods are deemed as actual 
// the example demonstrates how only primary key is passed when initializing an object
$book = Book::wakeUp(1);

var_dump($book->isTitleFilled());
// false

$book->fillTitle();

var_dump($book->isTitleFilled());
// true

The method isChanged responds to question if a new value was set during the session:

use \Bitrix\Main\Test\Typography\Book;

// object may have source value, but may not 
// this doesn't affect the further behaviour
$book = Book::wakeUp(['ID' => 1, 'TITLE' => 'Title 1']);

var_dump($book->isTitleChanged());
// false

$book->setTitle('New title 1');

var_dump($book->isTitleChanged());
// true

Such behaviour is applicable for new objects as well, until their values are stored in the database.

The method has checks, if an object has a field value - an actual value from the database or value, specified during the session. In fact, its an abbreviation from isFilled() || isChanged():

use \Bitrix\Main\Test\Typography\Book;

$book = Book::wakeUp(['ID' => 1, 'TITLE' => 'Title 1']);
$book->setIsArchived(true);

var_dump($book->hasTitle());
// true

var_dump($book->hasIsArchived());
// true

var_dump($book->hasIsbn());
// false