Two dimensional ruby array to java array

luislavena · December 29, 2010, 3:10am

I’m trying to convert a list of lists of strings in jruby to a
properly typed java array to send to a java function. I’m familiar
with the .to_java method on lists, but I’m not sure how to properly
type everything.

foo = [[“a”, “b”, “c”], [“d”, “e”, “f”]]

bar = foo.to_java(???) <---- what goes here

obj.setData(bar)

// in java
public void setData(String[][] args) { … }

What should I pass to to_java so I can call setData without getting a
type error?

joshs · December 29, 2010, 10:49am

Seems this is a recurrent issue, we should clarify it somehow, meanwhile
this spec is plenty of examples:

github.com

jruby/jruby/blob/master/spec/java_integration/types/array_spec.rb

require File.dirname(__FILE__) + "/../spec_helper"

java_import "java_integration.fixtures.ArrayReceiver"
java_import "java_integration.fixtures.ArrayReturningInterface"
java_import "java_integration.fixtures.ArrayReturningInterfaceConsumer"

describe "A Java primitive Array of type" do
  describe "boolean" do
    it "should be possible to create empty array" do
      arr = Java::boolean[0].new
      expect(arr.java_class.to_s).to eq("boolean[]")
      expect(arr).to be_empty
    end

    it "should be possible to create uninitialized single dimensional array" do
      arr = Java::boolean[10].new
      expect(arr.java_class.name).to eq("[Z")
      expect(arr).not_to be_empty
    end

This file has been truncated. show original

As a summary, argument symbols for the method to_java are aliases for
real
java classes, so :string is an alias for java.lang.String or :long is an
alias for the primitive type long, but there aren’t aliases for arrays,
so
we need to use those java classes directly with the syntax
Java::class_name.
So, to convert an array to a java array we can use this syntax:

.to_java(Java::java.lang.String[])

https://github.com/jruby/jruby/blob/master/spec/java_integration/types/array_spec.rb
Cheers

joshs · December 29, 2010, 12:45pm

I just wrote a small guide about this in my blog:

I hope it will be useful.

Cheers

On Wed, Dec 29, 2010 at 10:48 AM, David C.

joshs · December 29, 2010, 6:59pm

That’s exactly what I needed. Thank you for the blog post.

On Wed, Dec 29, 2010 at 3:44 AM, David C.