How to Call Clojure Functions from Java without Using RT Compilation?

Interoperating with Clojure from Java without RT Compilation

Despite outdated recommendations to utilize the clojure.lang.RT class for Clojure-to-Java interoperability, current approaches no longer require this method. This improved method involves compiling Clojure code into a standalone JAR and invoking it directly from Java. Here's a step-by-step guide:

1. Compile Clojure Code:

   • Create a Clojure file containing the functions you wish to call from Java.
   • Ensure the Clojure file includes the :methods keyword to generate static methods in Java.
   • Compile the file into a JAR using the command: lein jar.

2. Access Clojure Functions from Java:

   • Include the generated Clojure JAR in your Java project's classpath.
   • Create Java classes that import the necessary Clojure classes and invoke the static methods with the - prefix.

3. Example Clojure Code:

   (ns com.example.clojure)
   
   (defn binomial [n k]
     (let [a (inc n)]
       (loop [b 1
              c 1]
         (if (> b k)
           c
           (recur (inc b) (* (/ (- a b) b) c))))))

4. Example Java Code:

   import com.example.clojure;
   
   public class JavaCaller {
   
       public static void main(String[] args) {
           System.out.println("(binomial 5 3): " + clojure.binomial(5, 3));
           System.out.println("(binomial 10042, 111): " + clojure.binomial(10042, 111));
       }
   }

5. Run Java Program:

   • Compile the Java class with javac and generate a JAR with jar or an IDE.
   • Run the JAR to invoke the Clojure functions from Java.

This approach allows for seamless interoperability between Clojure and Java, eliminating the need for intermediate steps or complex compilation procedures.

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