Date: 09/16/05 (Java Web)    Keywords: php, java

In PHP, unlike Java or C++, $this has to be explicitly used to refer to variables within a class. The value of $this is determined by the context in which it is called. In certain situations $this may actually refer to the invoking class rather then the current class. This breaks object encapsulation. $this pseudo-variable is [...]

Source: http://blog.taragana.com/index.php/archive/php-encapsulation-surprises/