Purpose of object interface

In a small project like the one in the video, you can clearly get by without one. But in larger projects, and ones on which several people are collaborating, they become much more important. As he says, they specify which methods a class must implement. If you're running a project, and you want a programmer to write some classes that implement a set of methods, you could tell the programmer which methods to include in their classes, but it's much, much better to create an interface and have the programmer make each of their classes implement the interface. One benefit is that the compiler can then tell the programmer if they have implemented the correct set of methods. There's more, but yes, they come in very handy!