CODEWITHSUNDEEP
javaclojure
user1804599
user1804599

Reputation:

Is it possible for a class written in Java to implement a protocol written in Clojure?

I can only find stuff about the inverse; using Clojure to implement Java interfaces. However, I want to write a programme in Clojure and allow one to extend it with Java. For example:

# P.clj
(defprotocol P
  (f [a])
  (g [a b]))

# I.java
public class I implements P {
    public Object f(Object a) { … }
    public Object g(Object a, Object b) { … }
}

Also, how would I specify parameter types so I don’t have to use Object everywhere?

The only option I currently see is using dot-notation and relying on duck typing but I prefer compile-time verification of interface implementation on the Java side.

Upvotes: 8

Views: 295

Answers (2)

BillRobertson42
BillRobertson42

Reputation: 12883

As Isaac has already said, yes.

However, w/o a source representation, I think it's kind of a horsesh*t claim. Please note, I'm not referring to Isaac's answer when I say that. I'm referring to the way that Clojure works in this case.

If you need Java interop, you might want to stick with boring Java interfaces. I think it would also make it easier to interoperate w/other languages in the JVM too, as it is the least common denominator. I also think it makes it easier to communicate w/non Clojure developers.

Upvotes: 2

Isaac
Isaac

Reputation: 16362

Yes, it's quite possible, and just like that.

From the pertinent part of the docs:

defprotocol will automatically generate a corresponding interface, with the same name as the protocol, i.e. given a protocol my.ns/Protocol, an interface my.ns.Protocol. The interface will have methods corresponding to the protocol functions, and the protocol will automatically work with instances of the interface.

And, to answer your question:

A Java client looking to participate in the protocol can do so most efficiently by implementing the protocol-generated interface.

Upvotes: 7

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