javap可以打印出java的字节码：
-c Prints out disassembled code, i.e., the instructions that comprise the Java bytecodes, for each of the methods in the class. These are documented in the Java
Virtual Machine Specification @
http://docs.oracle.com/javase/specs/.
javap还可以打印出用户jni本地native调用的函数签名信息，不过只打印.class文件，不能打印.java文件，必须将.java文件编译为.class文件：
javap -classpath . ??.class
javap -classpath . -s -p ??.class