How to Retain Class Information for Java Objects Returned from C++ Using SWIG?

How can I retain class information for Java objects that are returned from C++ when using SWIG?

// Example code snippet showing how to use SWIG to wrap a C++ class.
class Example {
public:
    Example(int id);
    int getId();
};

// SWIG interface file example
%module example
%{
#include "example.h"
%}

%include "example.h"

To retain class information of objects bouncing from C++ to Java using SWIG (Simplified Wrapper and Interface Generator), you need to properly configure your SWIG interface files and use smart pointers in C++. This ensures that Java has access to the appropriate class metadata and methods through the Java Native Interface (JNI).

// SWIG example interface file using shared_ptr
%module example
%{
#include "example.h"
%}

%include <std_shared_ptr.i>
%shared_ptr(Example);
%include "example.h"

Causes

• Improper mapping of C++ classes to Java classes in SWIG interface files.
• Using raw pointers rather than smart pointers (e.g., std::shared_ptr) in C++ code can lead to loss of information during type conversions.

Solutions

• Ensure that your SWIG interface files correctly define the mappings for C++ classes to their respective Java classes.
• Utilize SWIG's `%shared_ptr` type to manage the C++ objects, which helps preserve class information when interacted with Java.
• Make use of SWIG typemaps for more complex data types that require specific handling when moving between C++ and Java.

Mistake: Neglecting to specify the shared pointer type in the SWIG interface file.

Solution: Always declare pointers as `%shared_ptr` in your SWIG interface to maintain proper object ownership and lifecycle.

Mistake: Trying to access C++ classes directly without utilizing appropriate accessor methods in Java.

Solution: Ensure you provide Java methods that wrap the necessary C++ functionality.