数据类型

[a284628487]

基本数据类型

/* Primitive types that match up with Java equivalents. */
typedef uint8_t  jboolean; /* unsigned 8 bits */
typedef int8_t   jbyte;    /* signed 8 bits */
typedef uint16_t jchar;    /* unsigned 16 bits */
typedef int16_t  jshort;   /* signed 16 bits */
typedef int32_t  jint;     /* signed 32 bits */
typedef int64_t  jlong;    /* signed 64 bits */
typedef float    jfloat;   /* 32-bit IEEE 754 */
typedef double   jdouble;  /* 64-bit IEEE 754 */

/* "cardinal indices and sizes" */
typedef jint     jsize;

#define JNI_FALSE   0
#define JNI_TRUE    1

值类型

typedef union jvalue {
    jboolean    z;
    jbyte       b;
    jchar       c;
    jshort      s;
    jint        i;
    jlong       j;
    jfloat      f;
    jdouble     d;
    jobject     l;
} jvalue;

类型签名

类型签名        Java 类型  

    类型签名        Java 类型  
    Z           boolean  
    B           byte     
    C           char     
    S           short    
    I           int  
    J           long     
    F           float    
    D           double   
    L fully-qualified-class ;       全限定的类    
    [ type      type[]

签名规则：( arg-types ) ret-type 例如Java方法：long f (int n, String s, int[] arr); 对应的类型签名: (ILjava/lang/String;[I)J

JNINativeInterface & _JNIEnv & JNIEnv

C 中使用 JNINativeInterface

struct _JNIEnv;
struct _JavaVM;
typedef const struct JNINativeInterface* C_JNIEnv;

#if defined(__cplusplus)
typedef _JNIEnv JNIEnv;
typedef _JavaVM JavaVM;
#else
typedef const struct JNINativeInterface* JNIEnv;
typedef const struct JNIInvokeInterface* JavaVM;
#endif

/*
 * Table of interface function pointers.
 */
struct JNINativeInterface {
    void*       reserved0;
    void*       reserved1;
    void*       reserved2;
    void*       reserved3;

    jint        (*GetVersion)(JNIEnv *);

    jclass      (*DefineClass)(JNIEnv*, const char*, jobject, const jbyte*,
                        jsize);
    jclass      (*FindClass)(JNIEnv*, const char*);
    // ...

C++ 中使用 JNIEnv

/*
 * C++ object wrapper.
 *
 * This is usually overlaid on a C struct whose first element is a
 * JNINativeInterface*.  We rely somewhat on compiler behavior.
 */
struct _JNIEnv {
    /* do not rename this; it does not seem to be entirely opaque */
    const struct JNINativeInterface* functions;

#if defined(__cplusplus)

    jint GetVersion()
    { return functions->GetVersion(this); }

    jclass DefineClass(const char *name, jobject loader, const jbyte* buf,
        jsize bufLen)
    { return functions->DefineClass(this, name, loader, buf, bufLen); }
    // ...

在开发中不论是使用C/C++，上述两个 Struct 都被定义成了 JNIEnv