JNI官方文档：https://docs.oracle.com/javase/7/docs/technotes/guides/jni/spec/jniTOC.html
JNI Functions
Chapter 4
This chapter serves as the reference section for the JNI functions. It provides a complete listing of all the JNI functions. It also presents the exact layout of the JNI function table.
Note the use of the term “must” to describe restrictions on JNI programmers. For example, when you see that a certain JNI function must receive a non-NULL object, it is your responsibility to ensure that NULL is not passed to that JNI function. As a result, a JNI implementation does not need to perform NULL pointer checks in that JNI function.
里面内容太多了，用时查官方文档吧