I need to choose between three programming languages C,C++ & Java for
developing data structures for a project which will require speed of
execution. Which will be a better option ?

What language do those doing the programming know best?

Will ths propagate over the internet?

How big and complex will the structure be in five years?

C++ was choosen by my magic eight ball.  Honest!

I chose Delphi

Initially because it had inline ASM
- but optimized .386 ASM is boring 
- so I reverted to optimized pseudo Pascal

RISC is tedious for low level programmers.

based purely on code execution speed and nothing else, C.  However,
you can do some very interesting things at compile time with C++
template meta-programming such that it might provide advantages
depending on the details.

Keep in mind that C is almost a proper subset of C++, so
theoretically, C++.  You don't *have* to use objects, the STL and
exceptions for it to be C++.