Problems with Compiling Generics.

[Suresh Rajadurai]

Hi Folks,

when I tried to compile the following code with

javac test.java

it gives the following message in the dos prompt:

Note: test.java used unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.


Then when I compiled with the following command:

javac -Xlint:unchecked test.java

it gives the following error messages:

javac: invalid flag: -xlint:unchecked
Usage: javac <options> <sourcefiles>
use -help for a list of possible options.


Could you guys PLEASE throw me some light on this annoying messages PLEASE.

import java.util.*;
 
class test
   {
 
public static List<String> getNameList()
   {
String [] sa = {"amy" , "audrey" , "Adam"};
List<String> list = Arrays.asList(sa);
return list;
   }
 
public static void main(String arg[])
   {
List<String> ls = getNameList();
Comparator c = Collections.reverseOrder();
Collections.sort(ls,c);
System.out.println(ls);
   }
   }

Thanks & regards

Suresh.

[Piet Verdriet]

Strange, when compiling your code like this:

javac -Xlint:unchecked test.java

I get the following message:

test.java:17: warning: [unchecked] unchecked conversion
found   : java.util.Comparator
required: java.util.Comparator<? super java.lang.String>
Collections.sort(ls,c);
                    ^
test.java:17: warning: [unchecked] unchecked method invocation: <T>sort(java.util.List<T>,java.util.Comparator<? super T> :wink:  in java.util.Collections is applied to (java.util.List<java.lang.String>,java.util.Comparator)
Collections.sort(ls,c);
                ^
2 warnings

It looks like you compiled your source file with two different compilers... Anyway, you should replace your line:

Comparator c = Collections.reverseOrder();

by:

Comparator<String> c = Collections.reverseOrder();

to make the warning disappear.

[Suresh Rajadurai]

Thank you.