Using Scala from Java: passing functions as parameters

Question

Consider the following Scala code:

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

Now in Ja

Answer 1

The easiest way for me is to defined a java interface like:

public interface JFunction {
  public B compute( A a );
}

Then modify your scala code, overloading setFunc to accept also JFunction objects such as:

object MyScala {
  // API for scala
  def setFunc(func: Int => String) {
    func(10)
  }
  // API for java
  def setFunc(jFunc: JFunction[Int,String]) {
    setFunc( (i:Int) => jFunc.compute(i) )
  }
}

You will naturally use the first definition from scala, but still be able to use the second one from java:

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

  public static final JFunction myFunc = 
    new JFunction() {
      public String compute( Integer a ) {
        return String.valueOf(a);
      }
    };

}