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The content from http://arm9.org.ru/redirect.php?tid=356&goto=lastpost
Android uses a structure “JNINativeMethod” to describe the JNI function as follows:
typedef struct {
const char* name;
const char* signature;
void* fnPtr;
} JNINativeMethod;
name: name of function in Java
signature: used to describe the parameters and return values of function
fnPtr: function pointer that point to C function。
Take some examples for second parameter:
“()V”
“(II)V”
“(Ljava/lang/String;Ljava/lang/String;)V”
“()” stands for the parameter, the later represents the return value.
Take “()V” as an example. It means “void Func();”
“(II)V” means “void Func(int, int)”;
Mapping table as below:
character C type Java type
V void void
Z jboolean boolean
I jint int
J jlong long
D jdouble double
F jfloat float
B jbyte byte
C jchar char
S jshort short
“array” denoted two characters as below:
[I jintArray int[]
[F jfloatArray float[]
[B jbyteArray byte[]
[C jcharArray char[]
[S jshortArray short[]
[D jdoubleArray double[]
[J jlongArray long[]
[Z jbooleanArray boolean[]
The above types discussed are standard. If the parameter is “class” type, start with “L” and end with “;”. Using “/” to separate package name and class name. And the parameter mapping to C is “object” except for String class. Its mapping is jstring.
Ljava/lang/String; String jstring
Ljava/net/Socket; Socket jobject
If Java function is placed in the embedded class, Using “$” as separated character.
i.e. “(Ljava/lang/String;Landroid/os/FileUtils$FileStatus;)Z”
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