org-mode: How to define then call a Java method using source blocks

Question

I have a super simple example where I have a list, a Java method and a call to this method. It looks like this:

#+name: animals
- dog
- cat
- guinea pig
- horse

#+name: does-contains-cat
#+begin_src java :results none
public boolean doesListContainsCat(List<String> list) {
    return list.contains("cat");
}
#+end_src

#+begin_src java :results value :var animalList=animals
doesListContainsCat(animalList);
#+end_src

Output → error: cannot find symbol doesListContainsCat(animalList)

When evaluating the first block it creates a Java file with a class and a main method containing my method… I know it is the expected behaviour but it is not the result I want. By keeping it as simple as that (if possible) I want to be able to display a result when evaluating the second block.

My other tries:

#+name: doesListContainsCat
#+begin_src java :results none :var list='("")
return list.contains("cat");
#+end_src

#+begin_src java :results value :var list=animals doesListContainsCat
return doesListContainsCat(list);
#+end_src

Output → error: incompatible types: unexpected return value

or with a #+CALL header:

#+CALL: doesListContainsCat(list=animals)

Output → error: incompatible types: unexpected return value

I know it's because the return type of the main method in Java is void.

How to make it work (and keep it simple) so that I can define a Java method inside a source block, call it later using another source block and display the result?

Since the first code block generates a separate class file, try to refer to your function the same way you would refer to any function in another class. 1. Use :classname header argument to set a class name within which your function is defined. 2. Make your function static. 3. Access to you function from the second code block using dot notation. — C. Aknesil
– C. Aknesil, Commented Sep 28, 2023 at 9:44
@C.Aknesil It doesn't work anyway since my first block does-contains-cat is encapsulated in a main method. @NickD Yes I have. — Nicryc
– Nicryc, Commented Sep 29, 2023 at 18:17

Nicryc · Accepted Answer · 2023-09-29 21:06:01Z

The best working solution I've found so far is:

#+name: animals
- dog
- cat
- guinea pig
- horse

#+name: does-contains-cat
#+begin_src java :results none :classname babel.java.A
public static void main(String[] args) {}
public static boolean doesListContainsCat(List<String> list) {
    return list.contains("cat");
}
#+end_src

#+begin_src java :results value :var animalList=animals[,0] :classname babel.java.B
return A.doesListContainsCat(animalList);
#+end_src

#+RESULTS:
: true

Defining two distinct classes with :classname and making a static call to my method as suggested by @C.Aknesil
Declaring an empty main method manually public static void main(String[] args) {} to force org-babel not to wrap my method doesListContainsCat in a main method
Using [,0] to tell org-babel to consider my list as a list and not a table

It's not the ideal solution but it works. I'm still looking for a better solution that doesn't involve the three workarounds listed above.

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