Given the following source listing, explain why the compiler is producing a warning at invocation to the list method and give a solution for removing the warning without resorting to @SuppressWarnings annotation.
public class JavaLanguagePuzzle3
{
public static void main( String[] args )
{
list( "1", 2, new BigDecimal( "3.5" ) );
}
private static <T> List<T> list( T... items )
{
return Arrays.asList( items );
}
}Warning:
Type safety: A generic array of Object&Serializable&Comparable<?> is created for a varargs parameter
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7 comments:
Remove the Generic Type <T>, and replace with a common supertype - in this case it would have to be "Object":
private static List<Object> list(Object... items )
{
return Arrays.asList( items );
}
You should choose a type. I'm not sure you can do that without class qualification:
JavaLanguagePuzzle3.<Object>list( "1", 2, new BigDecimal( "3.5" ) );
You can choose any common super type this way.
public static void main( String[] args )
{
Object[] items = new Object[]{"1", 2, new BigDecimal( "3.5")};
list( items );
}
private static List list( T... items )
{
return Arrays.asList( items );
}
Casting one of the arguments to a "lowest common denominator", such as (Object) "1", or (Serializable) 2 eliminates the warning.
Interestingly, the JavaC compiler does not emit a warning on the given code. Compiler bug? Language ambiguity?
Just cast one of the 3 arguments to Object, Serializable or Comparable.
The warning means something like 'I can't figure the type of T between these 3 possibilities'.
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