/usr/lib/jvm/java-1.5.0-gcj-5-amd64/include/jni.h is in gcj-5-jdk 5.3.1-14ubuntu2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/jvm/java-1.5.0-gcj-5-amd64/include/../../../gcc/x86_64-linux-gnu/5/include/jni.h