Question

Consider the following Scala code:

package scala_java
object MyScala {
  def setFunc(func: Int => String) {
    func(10)
  }
}

Now in Java, I would have liked to use MyScala as:

package scala_java;
public class MyJava {
    public static void main(String [] args) {
        MyScala.setFunc(myFunc);  // This line gives an error
    }
    public static String myFunc(int someInt) {
        return String.valueOf(someInt);
    }
}

However, the above does not work (as expected since Java does not allow functional programming). What is the easiest workaround to pass a function in Java? I would like a generic solution that works with functions having arbitrary number of parameters.

EDIT: Does Java 8 have any better syntax than the classic solutions discussed below?

Answer 1

You have to manually instantiate a Function1 in Java. Something like:

final Function1<Integer, String> f = new Function1<Integer, String>() {
    public int $tag() {
        return Function1$class.$tag(this);
    }

    public <A> Function1<A, String> compose(Function1<A, Integer> f) {
        return Function1$class.compose(this, f);
    }

    public String apply(Integer someInt) {
        return myFunc(someInt);
    }
};
MyScala.setFunc(f);

This is taken from Daniel Spiewak’s “Interop Between Java and Scala” article.