Static polymorphism with generics in Java -

i hoping create clean code can recursively dig collection , print first integer finds. coming c++ background approach looked this:

class test { static void print(integer i) {   system.out.println(i); }  static <t> void print(arraylist<t> arr) {   t entry= arr.at(0);   test.print (entry); }  static void test() {     arraylist<arraylist<integer>> arrayofarrayofint= create();     print( arrayofarrayofint ); } } 

unfortunately doesn't work.

one alternative give on static polymorphism , create function print(object o) , number of instanceof checks branch right behavior. way can done due java's type erasure or there more elegant approach?

the following method recursively dig object , return optional containing first integer finds, or optional.empty() if can't find one.

static optional<integer> firstint(object o) {     if (o instanceof integer)         return optional.of((integer) o);     if (o instanceof int[]) {         int[] array = (int[]) o;         return array.length > 0 ? optional.of(array[0]) : optional.empty();     }     if (o instanceof object[])         return firstint(arrays.aslist((object[]) o));     if (o instanceof iterable) {         (object o2 : (iterable<?>) o) {             optional<integer> result = firstint(o2);             if (result.ispresent())                 return result;         }     }     return optional.empty(); } 

you can using polymorphism, have create interface searchable this

interface searchable {     optional<integer> search(); } 

and create wrapper classes concrete types want able search. example:

public final class searchablelist<t extends searchable> extends abstractlist<t> implements searchable {      private final list<t> list;      searchablelist(list<t> list) {         this.list = list;     }      // rest omitted } 

however, such convoluted mess, , avoid it, preferring instanceof checks instead.