Objects like Character and Integer are pointers: the actual number stored in the bytes that are that variable's value represents an address in memory for the rest of the JVM's memory. So, it is possible and meaningful to set that number to an address that goes nowhere, which is what null is.
A primitive like int or char, however, has a number that is interpreted as a number (integer, or ASCII code), and there's no way to make it "not a number" because all that the memory can possibly store is numbers.
