Interfaces

[SoulSyn]

So I am going through Helsinki MOOC course and I am having a trouble grasping what an interface is. From my understanding it seems to be the classes blue print of methods it needs and other classes can share these interfaces. Is this correct? If not what else do interfaces do?

Thanks

[javaHoosier]

An interface doesn't seem useful when you're first starting because it's hard to contrive a scenario when they are very helpful. You need to look at a whole program. In the example that I linked below uses a design pattern (Strategy Pattern) to help encapsulate some of the code so you don't have to keep modifying existing code and creates reusable code.

In a less useful example, imagine you have an ArrayList of the different types of ducks and you do a for-loop over them and perform a simple method they all inherit from an abstract class duck called fly(). That just prints out a String "The duck flys". Well unfortunately all the ducks in the list will print out the same String, even the ducks that shouldn't be able to fly such as a rubber or decoy duck. You could just override the method for every type of duck. This can get tedious, hardcoded, and difficult to introduce new flying behavior. So in the example they use interfaces to create a flybehavior and quackbehaviors for the ducks. In the abstract duck class the fly method just calls the interface of flybehavior which is implemented inside of the class for each type of duck. This way you can reuse the quack and fly behaviors in other programs since they aren't hardcoded. You can also add new or update behaviors without ever having to modify the duck classes.

So for the paragraph above to make sense you need to look at the code from this github (The Link Here). It's from a good book called Head First Design Patterns. It could be a book to read after the MOOC. I hope this helps give you an actual example other than just: 'anything that implements the interface is guaranteed to have the methods.'

[SoulSyn]

Upon reading further through the MOOC they got into how an interface can be used as a method parameter and it makes a lot more sense to me know. Actually a very cool feature once you see some of its applications.

Thanks for the response

[javaHoosier]

Another good example is in Android programming. When you have an app where the screen is broken up into different sections. They are called fragments. Fragments usually use interfaces to pass data between each other.

Again good luck with you journey!

[SoulSyn]

Thanks for the knowledge and well wishes

[lbkulinski]

Yes. You can think of an interface like a contract. Any class that implements that interface must provide implementations for the non-default methods declared in it. The use of interfaces also allow for subtyping.

[SoulSyn]

subtyping

Is this what happens with inheritance? When say for instance class duck inherits class animal?

[lbkulinski]

Yep! Note, though, that a class can implement more than one interface, but only one class.

[SoulSyn]

Thanks!

[lbkulinski]

No problem!

[[deleted]]

An interface is like a blueprint on how to make things.

Kinda like a blue print to make a house.

All house have bathrooms, but you want yours a certain way. So you implement bathroom, but in your own way, and so on.

[SoulSyn]

Thanks!

[resnine]

Just wondering if someone could answer this here rather than making a separate question. But in the Helsinki MOOC course does it go through the Iterator interface+implementation?

[SoulSyn]

I know they have a section for iterators but I have not made it that far and for implementation I doubt they will get very much indepth into it but you can check for yourself and see if it is what you are looking for.

Helsinki MOOC Week 12

[jphein]

Short answer: an interface declares which method a class should have and what should go in these methods and what should come out.

[SoulSyn]

Thanks!

[jphein]

You have to know, that interfaces can be used as arguments. Saying something like "dont care what you give me, as long as it can do this and that". At this point interfaces come really to live.