Hi folks.

There might be a bit of confusion here about the exact Java types we're dealing with.

In Java:

• java.lang.Double is not the same as the primitive double type: it is an object wrapper for it
• java.lang.Double.class is the class of the object wrapper
• java.lang.Double.TYPE is the class of the corresponding primitive type

Matlab does not auto-convert the object wrapper types like java.lang.Double or java.lang.Double[]; it merely has a convenience display function that makes them look like primitive types.

>> java.lang.Double(42)
ans =
42.0
>> class(ans)
ans =
    'java.lang.Double'
>> java.lang.Double.class
ans =
    'java.lang.Double'
>> java.lang.Double.TYPE
ans =
double
>> class(ans)
ans =
    'java.lang.Class'

Nonono!!!

The site you cite,
 https://www.mathworks.com/help/matlab/ref/javaarray.html,
clearly says

ObjArr = javaArray(PackageName.ClassName,x1,...,xN) constructs an empty Java® array object for objects of the specified PackageName.ClassName class.

That is clear and that is not what is done in Octave.
What you cite:

> To create an array of primitive Java types, create an array of the equivalent MATLAB type, shown in the Conversion of MATLAB Types to Java Types table. See Conversion of MATLAB Argument Data.

is a tip only and it says nothing about the return type of javaArray, right?
The tip is not bad, but not always applicable,
as seen in you other link,

https://www.mathworks.com/matlabcentral/answers/96483-how-can-i-pass-a-ragged-array-of-java-primitive-types-to-a-java-function-from-matlab

It is about ragged arrays, which are supported by Java but not by Octave.

By the way, although maybe

> The ability to create Java primitive types is not available in MATLAB.

Octave HAS the ability to create arrays of primitive types.
It is an undocumented feature, that instead of a string,
one can pass a class and in particular Double.TYPE
as I pointed out below.
Maybe matlab can do so as well.


Also:
javaObject('java.lang.Double',42)
 yields

ans =

<Java object: java.lang.Double>


not just 42 for that reason.


A re

The problem is, that javaArray is a constructor invocation in matlab which means that the result is a java array.
In the example I provided, the result is an octave array or even an octave scalar, because boxing is applied.
The latter is wrong.

According to

http://de.mathworks.com/help/matlab/ref/javaarray.html?searchHighlight=javaArray

javaArray(cls,1) has to return a java array
i.e. for Octave an instance of octave_java
wrapping some new cls[1].

Consider
octave:16> dblCls=java_get('java.lang.Double', 'TYPE')
dblCls =

<Java object: java.lang.Class>

This is the class of the type double.

o=javaArray(dblCls,1)
 seems to be 0
and really:
class(o)
yields double instead of double[]



I know also the reason: javaArray is based on javaMethod
which performs boxing and unboxing.
That way, double[] is converted to a double scalar.