Exploring Advanced Language Features - Beginning Java 7 - page 274

The need for Wildcards
Supposethatyouhavecreateda List of String andwanttooutputthislist.Because
youmightcreatea List of Employee andotherkindsoflists,youwantthismethod
to output an arbitrary List of Object . You end up creating Listing 3-55 .
Listing 3-55. Attempting to output a List of Object
import java.util.ArrayList;
import java.util.List;
class OutputList
{
public static void main(String[] args)
{
List<String> ls = new ArrayList<>();
ls.add("first");
ls.add("second");
ls.add("third");
outputList(ls);
}
static void outputList(List<Object> list)
{
for (int i = 0; i < list.size(); i++)
System.out.println(list.get(i));
}
}
Nowthatyou'veaccomplishedyourobjective(orsoyouthink),youcompile Listing
3-55 via javac OutputList.java .Muchtoyoursurprise,youreceivethefollow-
ing error message:
OutputList.java:12: error: method outputList in class Out-
putList cannot be applied to given
types;
outputList(ls);
^
required: List<Object>
found: List<String>