how do I correctly write following class declaration in Java?
public class BinarySearchTree<T extends BinarySearchNode<E implements Comparable<E>>> implements Iterable<E>
Basically, I am trying to create a BinarySearchTree of any class T that inherits BinarySearchNode of a Comparable datatype E (And my BinarySearchTree should also be Iterable).
How can I properly declare that class in Java? Thanks!
public class BinarySearchTree<T extends BinarySearchNode<E>, E extends Comparable<E>> implements Iterable<E>
The type parameter E needs to be defined separately from the node type, even if it ends up looking redundant: BinarySearchTree<BinarySearchNode<String>, String>. Java won't let you directly access a generic parameter of a generic type.
Also, note that generic parameters always use "extends" even with interfaces.
With Generics in Java, you will only use extends. So, essentially your method decoration would become:
public class BinarySearchTree<T extends BinarySearchNode<E extends Comparable<E>>> extends Iterable<T>
Even for those classes that implement an interface, generics will use extends. The only other syntax for generics is super if you are looking at the inheritance from the opposite direction
class A<T extends B<E extends C>>. Besides, Iterable is an interface, so you must use the keyword implements if the class acutally implements it, it cannot be extended.
Iterableon the values i.e.Einstead of on the node?E extends Comparable<E>forE extends Comparable<? super E>. This would allow you to have a tree of i.e.DogwithDogbeing a subclass ofAnimalandAnimalbeingComparable. I mean that you could use thecompareTomethod from one ancestor of the element type of your tree, and you shouldn't need to implementcompareToinDog(using the one fromAnimalwould suffice, if it's good enough).<E>to<? super E>. If you are interested on this topic, you should read about PECS.