Improvement suggestion for java.lang.Iterable

Question

The current design limits each container to one collection. Wouldn't it be better to define java.lang.Iterable as
interface Iterable<T> {
Iterator<T> iterator(Class<T> class)
Then a conainer could hold multiple collections, as long as each collection contains different types.
Then I could write
class Zoo
implements Iterable<Tiger>,
implements Iterable<Elephant> {
Iterator<Tiger> iterator(Class<Tiger> class) ...
Iterator<Elephant> iterator(Class<Elephant> class) ...
and the compiler would be able to handle this:
for (Tiger tiger : zoo) .. give me all Tigers
for (Elephant elephant : zoo) .. give me all Tigers

Answer 1

The current design limits each container to one collection. Wouldn't it be better to define
java.lang.Iterable as
interface Iterable<T> {
Iterator<T> iterator(Class<T> class)
}If you were to do that, none of the existing Collection types could implement it without breaking backward compatibility.
Then I could write
class Zoo
implements Iterable<Tiger>,
implements Iterable<Elephant> {Unfortunately it's not possible to implement the same interface twice with different type arguments. I say unfortunately because I believe one of my own API designs would benefit from that capability, if it were possible.
and the compiler would be able to handle this:
for (Tiger tiger : zoo) .. give me all Tigers
for (Elephant elephant : zoo) .. give me all TigersYou can still do this:
class Zoo {
    Collection<Tiger> tigers() { ... }
    Collection<Elephant> elephants { ... }
for (Tiger tiger : zoo.tigers())  ...
for (Elephant elephant : zoo.elephants()) ...Mark