Java 8 需要强制转换，而 Java 7 不需要 - enum.getClass/getDeclaringClass

我意识到Java 8仍处于Beta阶段，但这个让我感到奇怪：

public class Fields<C extends Enum<C>> {

    public Fields(Set<C> columns) {
        // A sample column used to find the universe of the enum of Columns.
        C sampleCol = columns.iterator().next();
        // Java 8 needs a cast here.
        Set<C> allColumns = EnumSet.allOf((/*Class<C>)*/ sampleCol.getClass());
        // ... there's more to this that I've deleted.
    }

}

错误显示为：

error: incompatible types: inferred type does not conform to equality constraint(s)
            Set<C> allColumns = EnumSet.allOf(sampleCol.getClass());
    inferred: C
    equality constraints(s): C,CAP#1
  where C is a type-variable:
    C extends Enum<C> declared in class Test.Fields
  where CAP#1 is a fresh type-variable:
    CAP#1 extends Enum from capture of ? extends Enum

这是 Java 8 的 bug 还是新功能？