Using the Raw Native Interface

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Accessing Fields

In many real-world examples the Java class will have fields that we want to modify from native code and this is pretty straightforward. Imagine we have a class that looks like:

    class FieldDemo
    {
        int x;
        int y;
        int z;

        public native void SetFields();
    }

This is the msjavah generated header file:

	/* DO NOT EDIT THIS FILE - it is machine generated */
	#include <native.h>
	/* Header for class FieldDemo */
	
	#ifndef _Included_FieldDemo
	#define _Included_FieldDemo
	
	typedef struct ClassFieldDemo {
	#pragma pack(push,1)
	    int32_t MSReserved;
	    long x;
	    long y;
	    long z;
	#pragma pack(pop)
	} ClassFieldDemo;
	#define HFieldDemo ClassFieldDemo
	
	#ifdef __cplusplus
	extern "C" {
	#endif
	__declspec(dllexport) void __cdecl FieldDemo_SetFields(struct HFieldDemo *);
	#ifdef __cplusplus
	}
	#endif
	#endif

So here the ClassFieldDemo structure defines fields for modifying x, y, z so for example if we wanted to set x, y, z to 42, 43 and 44 we'd write:

    void cdecl FieldDemo_SetFields(struct HFieldDemo *phThis)
    {
        phThis->x = 42;
        phThis->y = 43;
        phThis->z = 44;
    }

One thing to note is how the Java "int" maps to a "long" on the native side, here's a table of how all the types map.

Java	C
boolean	long
byte	long
char	long
double	double
float	float
int	long
long	int64_t
short	long