jlong

jlong is a data type defined by the Java Native Interface (JNI) in the header jni.h. It represents the Java long primitive, a 64-bit signed integer. In native code, jlong is used for parameters and return values that correspond to Java long values, ensuring consistent cross-language behavior when Java code calls native methods or native code invokes Java methods. The size of jlong is defined as 64 bits on all platforms supported by JNI, matching Java's 64-bit long, regardless of the native compiler's long size.

In practice, jlong is typically defined as a 64-bit signed integer typedef, such as long long on many compilers, but the exact underlying C type is implementation-defined to preserve portability. When declaring native methods, use jlong for parameters and return values that map to Java long. Example: JNIEXPORT jlong JNICALL Java_com_example_MyClass_doubleLong(JNIEnv* env, jobject obj, jlong value) { return value * 2; }.

To print or log a jlong value, cast to a 64-bit type and use a format specifier appropriate for that type. For instance, printf("%lld", (long long) value) or use PRId64 from inttypes.h for portability.

Related JNI types include jint (32-bit int), jshort, jbyte, jboolean, and jsize, which cover other primitive Java types and array lengths. The jlong type exists to maintain a stable, platform-agnostic representation of Java's long in native code. See also: Java Native Interface, jni.h, Java long.