How to Integrate Java into C Applications: Can You Run Java Code on the Fly?

Integrating Java into C Applications

To extend the functionality of a C application, incorporating a Java component may be desirable. While this has been achieved with Python, it seems like there hasn't been a clear solution for Java integration.

JNI and Java Class Usage from C

Java Native Interface (JNI) is a potential solution, but it typically assumes a full Java program utilizing Java classes. However, for this case, the goal is to utilize Java classes from within the C application.

Compiling and Evaluating Java Code on the Fly

The desired functionality involves compiling and executing Java code during runtime (like a scripting language) using JNI or a similar mechanism.

Example Java Code

<code class="java">import c4d.documents.*;

class Main {
  public static void main() {
    BaseDocument doc = GetActiveDocument();
    BaseObject op = doc.GetActiveObject();
    if (op != null) {
      op.Remove();
    }
  }
}</code>

Solution: Embedded JVM

The solution lies in embedding a Java Virtual Machine (JVM) within the C application. Oracle's reference book provides the necessary information. The key steps involve:

• Including and initializing JVM arguments (JavaVM and JNIEnv)
• Initializing the JVM by calling JNI_CreateJavaVM()
• Using JNI to invoke Java methods (e.g., jclass, jmethodID, and jmethod)
• Destroying the JVM using JNI_DestroyJavaVM()

This allows for more sophisticated operations, such as custom class loaders, providing the necessary integration of Java capabilities into the C application.

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