How can you make applications in C or Java?

Yes, and actually it’s a good option for creating performant cross-platform code for a mobile app. Both iOS and Android toolchains will compile and link C. Both require a little glue code here and there in Objective C and Java, but for the most part both have:

• POSIX libraries
• libc
• OpenGL-ES C API
• libz

I honestly think network code on iOS is easier in C using the built-in POSIX/BSD socket lib than it is using the higher-level iOS API.