You've got it backwards. Rust is lower level than Java, so Java would be calling Rust, not the other way around.
Rust isn't aiming to displace Java. They're two different levels of abstraction. It's the same with Python. Rust isn't aiming to displace Python just as Java isn't aiming to displace Python either.
Rust one day could displace C++, but the odds are low, because in response to Rust C++ has stepped up its game and has changed as a language drastically. Most modern C++ features are concepts from Rust.
Rust isn't aiming to displace Java. They're two different levels of abstraction. It's the same with Python. Rust isn't aiming to displace Python just as Java isn't aiming to displace Python either.
Rust one day could displace C++, but the odds are low, because in response to Rust C++ has stepped up its game and has changed as a language drastically. Most modern C++ features are concepts from Rust.