PHP Classes, Interfaces, & Traits

Below are some general characteristics of classes, interfaces, and traits. The lists are incomplete and not detailed but capture some important features to understand them.

CLASSES

Can:

• CAN have a constructor
• CAN have zero or more data members and/or methods
• CAN be used to instantiate objects
• CAN only extend a maximum of one Class (abstract or concrete)
• CAN implement many Interfaces
• CAN use many Traits

Cannot:

• CANNOT have abstract methods
• CANNOT have nested Classes

TRAITS

Can:

• CAN have a constructor
• CAN have data fields
• CAN have methods
• CAN use many Traits

Cannot:

• CANNOT extend Classes or implement Interfaces
• CANNOT have abstract methods
• CANNOT be used to instantiate objects

INTERFACES

Can:

• CAN extend many Interfaces
• CAN have only function definitions
• CAN only be implemented by an abstract or concrete Class

Cannot:

• CANNOT have a constructor
• CANNOT have data members
• CANNOT have abstract methods
• CANNOT be used to instantiate objects
• CANNOT extend Classes or use Traits