Doubt - PHP Object Oriented / Pattern Strategy:

Hello, I have a question on how to use the standard strategy in php. How can I type a variable in php to be an interface as it is done in java
Waltever variavel , whose interface is Whatever?

I have a class that has a class that implements this interface and in my abstract class I can from some tipa method a variable as an interface so that I can in another class that extends the abstract class and instance in the variable any class that ultilize the interface? Home or in fact it is better not to use interface in the standard strategy of PHP.