a question about directory structure of libjava

Hi.

I'm new to gcj. And I'm reading the source code in the directory of
libjava. I'm a little confused by the structure of the directory.

I found that there often exists two java files, which have much
differnce in content, having the same name in different directories.
Such as,

libjava/java/lang/Class.java
libjava/classpath/java/lang/Class.java

Will both of them be used?

I also found C++ files libjava/java/lang/Class.h, which declares the
class Class in C++ corresponding to Class.java.
And libjava/java/lang/natClass.cc, which implements the native methods.

 But there's often no implementation of methods in C++.
 Dose the method code come from the Java file? How dose this happen?


Thank you.

Gmmajia