jdouble

jdouble is a JNI type used in native code to represent the Java language’s double primitive. It is defined in the Java Native Interface (JNI) headers as a typedef alias to the standard C type double. In JNI, Java’s double maps to jdouble, while other primitive types have corresponding aliases such as jint, jlong, and jboolean. Arrays of doubles in Java correspond to jdoubleArray in native code; elements can be accessed with GetDoubleArrayElements, ReleaseDoubleArrayElements, or GetDoubleArrayRegion.

As a primitive alias, jdouble is not an object but a direct 64-bit floating-point value on most platforms. When writing native methods, parameters and return values use jdouble in place of Java’s double. For example, a native method signature in C might declare a parameter as jdouble value and return a jdouble. Works similarly for methods that operate on arrays: a Java double[] is represented as a jdoubleArray, and individual elements are handled via the JNI array access functions.

Common usage patterns involve converting between Java and native representations without duplicating data unnecessarily. Native code that manipulates arrays typically obtains a pointer to the array elements, performs computations, and then releases the elements back to the JVM, optionally committing changes. It is important to follow proper JNI practices, including exception checks, local references management, and correct handling of array access to avoid memory leaks or crashes.

In summary, jdouble is the JNI-defined alias for the Java double type used in native code, enabling seamless passage of 64-bit floating-point values between Java and C or C++ through the JNI interface.