Mainframe, MVS and zOS Discussion

java.io.File will work perfectly on a mainframe, because it's a part of the Java standard, so it's also platform-independent. However if you want to use some third-party libraries for your file handling, they might not work on a mainframe.

Hi,

Sure. Since Java compiles to a bytecode, which is processor-independent, you can write your programs and even compile them on your local PC and then transfer that compiled binaries to a mainframe and they would work there. But some Java libraries use native code libraries, for example IBM JZOS ...

Depends on the tasks you want to accomplish with Java.
I would recommend:
- Java Stand-alone Applications on z/OS, especially volume II:
http://www.redbooks.ibm.com/abstracts/sg247291.html
If you need to work with DB2 via Java then you might want to read:
- DB2 for z/OS and OS/390: Ready for Java ...