Как переводить ссылочные типы в примитивные и наоборот?

In Java, auto-boxing and unboxing are used to convert between reference types (wrappers) and primitive types.

Example:

Integer wrapper = 10;       // auto-boxing: int -> Integer
int primitive = wrapper;    // unboxing: Integer -> int

You can also explicitly convert:

Integer wrapper = Integer.valueOf(5);
int primitive = wrapper.intValue();

The principle is similar for other types (Double, Boolean, etc.).