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https://issues.apache.org/jira/browse/LANG-819?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13862742#comment-13862742
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Shevek commented on LANG-819:
-----------------------------
You misunderstand type bounds. Anyway, here is an example.
public class EnumTest {
enum Foo {
A, B, C;
}
public static void main(String[] args) {
Set<? extends Foo> set = EnumSet.allOf(Foo.class);
// set.add(Foo.B); // Fails to compile: Set is typed read-only. See
references above.
EnumUtils.generateBitVector(Foo.class, set); // Also fails to
compile, even though legitimate.
generateBitVector(Foo.class, set); // Compiles fine, as method has
correct type.
}
// Note method signature now has correct type for a method which only reads
from the given set.
public static <E extends Enum<E>> long generateBitVector(Class<E>
enumClass, Iterable<? extends E> values) {
long total = 0;
for (E constant : values)
total |= 1 << constant.ordinal();
return total;
}
}
> EnumUtils.generateBitVector needs a "? extends"
> -----------------------------------------------
>
> Key: LANG-819
> URL: https://issues.apache.org/jira/browse/LANG-819
> Project: Commons Lang
> Issue Type: Bug
> Components: lang.*
> Affects Versions: 3.0.1
> Reporter: Shevek
> Priority: Minor
>
> public static <E extends Enum<E>> long generateBitVector(Class<E>
> enumClass, Iterable<E> values) {
> Should be Iterable<? extends E>.
> This is because although no subclasses of E can exist, the "? extends" is a
> common idiom for marking the collection as readonly, or not "owned" by the
> current object.
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