I've just earned my Master of C.S. from a French Grande Ecole. As a
was looking for a job in Java/C++ a firm made this proposition :

1/ they offer me the training in mainframes env
2/ i'll be working with the following technologies :
IBM Z serie, MVS, Cobol or PL/1 or C or C++

My first thought was : this is a trap from where i won't be abble to escape: 
mainframes are rather old and innatractive, Cobol and PL/1 are not charming etc...
But i discovered that there's a demand for JAVA+COBOL on IBM
mainframes (since IBM is involved in JAVA...) so i'm plaining to take
the job for 1-2 years and then ask for a training in J2EE and move to
JAVA on mainframe.

This is my idea.

To make things clear :
i'd like to have the following informations:
1/ is it likely to have a strong demand for JAVA on mainframe now and
in the future ?
2/ is my career plan feasible ?
3/ what technical questions should i ask during the final interview
(as i know nothing about mainframes, i'm a bit confused about what is
important to know)
4/ all other informations that you judge relevant...

My Advice

- If you are not getting a lot of job offers take this one.
- If you find you are spending all your time on legacy technologies 
  make sure to learn some of the newer technologies (JAVA) If this, means
  doing it on your own PC in your spare time , I would say do it.
- Some of the legacy technologioes may be around for some years to come.
  Both IBM  mainframe and IBM Midrange technology will be around for the next 
  10 to 20 twenty years. I would suggest knowing a blend of Legacy and "new"
  technology.
- Regarding the company's offer to train you on the mainframe, I would make 
  sure to get specifics on this (who does the training, how you will learn 
  it , etc)    

  Regards
  Mongolia

I agree with Mongolia, but would like to add this :-

The company wants to train you on legacy systems
- that means that they want to invest money in getting you to learn skills
- which suggests that they are 
  a) incredibly stupid 
or 
  b) finding it hard to find legacy system programmers

Those mainframes will hang around for some time, mostly they will
become Servers for large Client Server systems (well they already
are).

It might be a good idea to request Java training/involvement, on the
grounds that it will help understanding the interface.

If the company is reputable and is offering a reasonable salary, then
it could be a good opportunity to develop some niche skills, which
will become increasingly valuable as the old mainframers retire or
lose interest.

Think of it this way, what would you prefer to do, write SQL queries
or write an SQL server ?