Question

I am attempting to interop to this simple scala code, but am having some troubles.

package indicators

class DoubleRingBuffer(val capacity:Int=1000) {
  var elements = new Array[Double](capacity);
  private var head=capacity-1
  private var max=0

  def size ():Int = {
    return max+1
  }

  def add(obj:Double):Double = {
    head-=1
    if (head<0) head=capacity-1
    return set(max+1,obj)
  }

  def set(i:Int,obj:Double):Double = {
    System.out.println("HI")
    if (i>=capacity || i<0)
      throw new IndexOutOfBoundsException(i+" out of bounds")
    if (i>=max) max=i
    var index = (head+i)%capacity
    var prev = elements(index)
    elements(index)=obj
    return prev
  }

  def get(i:Int=0):Double = {
    System.out.println("size is "+size())
    if (i>=size() || i<0)
      throw new IndexOutOfBoundsException(i+" out of bounds")
    var index = (head+i)%capacity
    return elements(index)
  }    
}

In clojure, i do this

(import 'indicators.DoubleRingBuffer)
(def b (DoubleRingBuffer. 100))
(pr (.size b)) ;;ERROR: No matching field found: size for class indicators.DoubleRingBuffer
(pr (.get b 33)) ;;returns 0: should throw an index out of bounds error!
(pr (.get b 100)) ;;throws index out of bounds error, as it should

In addition, i do not get any output to the console! Testing this code using scala works as expected. Whats going on here and how can i fix it so that clojure can use the scala code?

Answer 1

Try these in REPL:

(class b) will probably tell you it’s indicators.DoubleRingBuffer.

(vec (.getDeclaredMethods (class b))) will give you a vector of all methods declared in your class as if it was a Java class, so you can see their signatures.

Now, call your methods as seen in the signatures, with these method names and parameters.

I have a feeling the problem is in Scala’s dealing with default value for method parameter.

EDIT: As OP described in a comment, it isn’t.

If that doesn’t work you can try to decompile your Scala bytecode to Java to find out how does DoubleRingBuffer class look like.