What is the relationship between threads (in a java or a C++ program) and number of cores in the CPU?

What is the relationship between threads (in a java or a C++ program) and
number of cores in the CPU?

Can someone shed some light on it?
i7 can run 8 threads but i am pretty sure we can make more than 8 threads
in JAVA or C++(not sure though). I have a i5 and while studying
concurrency i made 10 threads for assignments. I am just trying to
understand how Core rating of CPU is related to threads.