Game Development Reference
In-Depth Information
[ type
type[ ] array
(arg-types) ret-type
(method) return type
V
void
For example, the Java method
long JavaMethod1(int number, String str, int[] intarray1);
has the following type signature:
(ILjava/lang/String;[I)J
Another example is the
AddRotation()
function from the Orientation class.
void AddRotation(float AngleIncrementDegrees)
The signature type for this function would be
(F)V
The
F
would represent the float input parameter, and the
V
would represent the void return type.
Calling Native Code from Java and Accessing Java Methods from
Native Code
To call a native function from Java code, you would use the native function name without the
mangled prefix with the extra identifying information. For example, to call the native function
AddRotationNative()
shown in Listing 11-5, you would use the code shown in Listing 11-4.
Listing 11-4. Calling Native Code from Java
void AddRotationToObject(Orientation O, float AngleAmount)
{
AddRotationNative(O, AngleAmount);
}
The native function
AddRotationNative()
shown in Listing 11-5 calls the
AddRotation()
function for
the Orientation object that is passed into the function and held in the
Orient
variable.
The
AddRotationNative()
function does the following:
Gets the class of the Java object
Orient
by calling the
GetObjectClass()
JNI
function and assigns it to the
OrientationClass
variable
1.
Gets the method id of a specific function by calling the
GetMethodID()
JNI function with parameters including the function name, which is
"AddRotation"
; the function signature type, which is
"(F)V"
; and the Java
class object that contains the function, which is
OrientationClass
. This
method id is assigned to the
MethodID
variable.
2.
