Is it even possible?
if you mean an anonymous function, and are using a version of Java before Java 8, then in a word, no. (Read about lambda expressions if you use Java 8+)
However, you can implement an interface with a function like so :
Comparator<String> c = new Comparator<String>() {
int compare(String s, String s2) { ... }
};
and you can use this with inner classes to get an almost-anonymous function :)