CODEWITHSUNDEEP
javascalanetbeansinterop
capkidd
capkidd

Reputation: 11

My Scala methods do not return values to Java code

This is a Scala module:

package xpf

import java.io.File
import org.jdom.Element
import org.jdom.input.SAXBuilder

object xmlpf {
  def load_file(filename: String): Element = {
    val builder = new SAXBuilder
    builder.build(new File(filename)).getRootElement
  }
}

And here is Java code, calling the method from Scala above:

package textxpf;

import org.jdom.Element;

public class Main {
    public static void main(String[] args) {
        Element root = xpf.xmlpf.load_file("/home/capkidd/proj/XmlPathFinder/Staff.xml");
        System.out.println(root.getName());
    }
}

Running java main procedure I see

run:
Exception in thread "main" java.lang.NullPointerException
        at textxpf.Main.main(Main.java:8)
Java Result: 1
BUILD SUCCESSFUL (total time: 0 seconds)

Exploring the problem I found that I cannot return any value of any type from any Scala method to the Java code that called it.

I use NetBeans 6.9.1 with Scala 2.8.1 plugin. scala-library.jar and jdom.jar are properly plugged to the project.

What am I doing wrong? Has anybody any idea?

Upvotes: 0

Views: 699

Answers (2)

Dean Wampler
Dean Wampler

Reputation: 2151

I tried a similar program with no problems:

// ms/MyObject.scala
package ms
object myObject {
  def foo(s: String) = s
}

// mj/MyObject2.java
package mj;
public class MyObject2 {
  public static void main(String[] args) {
    System.out.println(ms.myObject.foo("hello"));
  }
}

I compiled both files, then "scala -cp . mj.MyObject2". Works fine with scala 2.8.1.final. Does this example work in your setup?

So, I wonder if it's some sort of environment issue, such as picking up a stale build of the Scala class? Have you tried a clean build from scratch? Is your runtime class path correct?

Upvotes: 1

Erik Engbrecht
Erik Engbrecht

Reputation: 3164

Try this and then debug accordingly:

package xpf

import java.io.File
import org.jdom.Element
import org.jdom.input.SAXBuilder

object xmlpf {
  def load_file(filename: String): Element = {
    val builder = new SAXBuilder
    val re = builder.build(new File(filename)).getRootElement
    if (re == null) throw new NullPointerException("the root element is null!")
    re
  }
}

Upvotes: 2

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