import java.util.*; import java.util.function.*; class MyTest { void foo(String[] strings){ final List> list = map2List(strings, str -> s -> assertEquals(str, s)); } static List map2List(T[] array, Function mapper) { return null; } static boolean assertEquals(Object o1, Object o2) { return false; } static boolean assertEquals(String o1, String o2) { return false; } }