Java – generics and classes >, EnumSet. allOf(class)vs class. getEnumConstants()

I have the following beanvalidation code that works properly and allows you to validate a bean annotation with:

@EnumValue(enumClass = MyTestEnum.class)
  private String field;

  public enum MyTestEnum {
    VAL1,VAL2;
  }

It is validated only when the field value is "val1" or "val2"

public class EnumNameValidator implements ConstraintValidator<EnumValue,String> {

  private Set<String> AVAILABLE_ENUM_NAMES;

  @Override
  public void initialize(EnumValue enumValue) {
    Class<? extends Enum<?>> enumSelected = enumValue.enumClass();
    Set<? extends Enum<?>> enumInstances = Sets.newHashSet(enumSelected.getEnumConstants());
    AVAILABLE_ENUM_NAMES = FluentIterable
            .from(enumInstances)
            .transform(PrimitiveGuavaFunctions.ENUM_TO_NAME)
            .toImmutableSet();
  }

  @Override
  public boolean isValid(String value,ConstraintValidatorContext context) {
    if ( value == null ) {
      return true;
    } else {
      return AVAILABLE_ENUM_NAMES.contains(value);
    }
  }

}

What I don't understand is why my first attempt failed Use enumselected instead of the following code getEnumConstants()：

Set<? extends Enum<?>> enumInstances = EnumSet.allOf(enumSelected);

IntelliJ 12 does not highlight any errors, but the compiler says:

java: method allOf in class java.util.EnumSet<E> cannot be applied to given types;
  required: java.lang.Class<E>
  found: java.lang.Class<capture#1 of ? extends java.lang.Enum<?>>
  reason: inferred type does not conform to declared bound(s)
    inferred: capture#1 of ? extends java.lang.Enum<?>
    bound(s): java.lang.Enum<capture#1 of ? extends java.lang.Enum<?>>

I don't understand the problem. I also have that code working normally:

private static <T extends Enum<T> & EnumAlternativeName> T safeGetByAlternativeName(Class<T> enumClass,String alternativeName) {
    for ( T t : EnumSet.allOf(enumClass) ) {
      if ( t.getAlternativeName().equals(alternativeName) ) {
        return t;
      }
    }
    return null;
  }

Solution

Is my guess? Extended enum where t is the same

For example, consider the following code:

static enum MyEnum {}
static class EnumValue<T extends Enum<T>> {
    Class<T> enumClass;
    EnumValue(Class<T> enumClass) {
        this.enumClass = enumClass;
    }
    Class<T> enumClass() { return enumClass; }
}

These lines compile:

EnumValue<?> enumValue = new EnumValue(MyEnum.class); // raw constructor
Set<? extends Enum<?>> enumInstances = EnumSet.allOf(enumValue.enumClass());

Because we know these two are in enumvalue The T in enumclass () is the same, but this does not:

EnumValue enumValue = new EnumValue(MyEnum.class);
Class<? extends Enum<?>> enumSelected = enumValue.enumClass();
Set<? extends Enum<?>> enumInstances = EnumSet.allOf(enumSelected);

Because you have used class > as an intermediate step