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Asked: 2026-06-04T20:21:06+00:00

Background The FreeLing API defines an interface that does not adhere to standard Java

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Background

The FreeLing API defines an interface that does not adhere to standard Java naming conventions. For example:

package freeling;

public class sentence extends ListWord {
  public void set_parse_tree(parse_tree arg0) {

The interface is defined using SWIG, which is similar to IDL:

class sentence : public std::list<word> {
 public:
  sentence(void);

  void set_parse_tree(const parse_tree &);

Problem

Academically speaking, how would you map the interface to conventional Java naming standards (e.g., class Sentence and setParseTree( parseTree arg0 ))?

Ideas

  1. Convert the 650+ line interface file manually (and send a patch to the developers).
  2. Regex search and replace voodoo (using vi): :1,$s/_\([a-z]\)/\u\1/g
  3. Create wrapper classes from the 53 auto-generated Java source files.

Thank you!

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1 Answer

  1. Editorial Team

    SWIG provides a %rename directive that allows the names to be different in the client and implementation languages. But doing this will nearly double the length of the interface file.

    Actually, SWIG provides bulk renaming. See the documentation

    5.4.7.2 Advanced renaming support

    While writing %rename for specific declarations is simple enough, sometimes the same renaming rule needs to be applied to many, maybe all, identifiers in the SWIG input. For example, it may be necessary to apply some transformation to all the names in the target language to better follow its naming conventions, like adding a specific prefix to all wrapped functions. Doing it individually for each function is impractical so SWIG supports applying a renaming rule to all declarations if the name of the identifier to be renamed is not specified:

    %rename("myprefix_%s") ""; // print -> myprefix_print

    This also shows that the argument of %rename doesn’t have to be a literal string but can be a printf()-like format string. In the simplest form, "%s" is replaced with the name of the original declaration, as shown above. However this is not always enough and SWIG provides extensions to the usual format string syntax to allow applying a (SWIG-defined) function to the argument. For example, to wrap all C functions do_something_long() as more Java-like doSomethingLong() you can use the "lowercamelcase" extended format specifier like this:

    %rename("%(lowercamelcase)s") ""; // foo_bar -> fooBar; FooBar -> fooBar

    Some functions can be parametrized, for example the "strip" one strips the provided prefix from its argument. The prefix is specified as part of the format string, following a colon after the function name:

    %rename("%(strip:[wx])s") ""; // wxHello -> Hello; FooBar -> FooBar

    My recommendation is just to leave it as-is. You’re calling C++ functions, they have C++ names. If anything, this helps you remember that you’re calling out to C++ and need to follow C++ rules for object lifetime management, there’s a slight JNI performance penalty, etc.

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