具有 enum 类型字段的 Java 枚举

Question

Not sure how to phrase the question so please feel free to update it. I have a complex enumeration which references other enumerations based on the enumeration value, like this:

public enum EFormSw {

    OBJ_KEY_LIST("Object Keys", EObjKeyType.class),
    OBJ_NOTE_LIST("Object Notes",  EObjNoteType.class);

public final String label;
public final Class</*"E is an Enum"*/> enumType;

// Constructor...

What I want to be able to do in another class is to write something like

EFormSw.OBJ_KEY_LIST.enumType.values().someThingElse().

Which is only possible if its clear by the field type that this is an enumeration.

Is there any way to achieve this at all?

Answer 1

You can make enumType a Class<? extends Enum<?>> Class<? extends Enum<?>> :

enum EFormSw {

  OBJ_KEY_LIST("Object Keys", EObjKeyType.class),
  OBJ_NOTE_LIST("Object Notes", EObjNoteType.class);

  private final String label;
  private final Class<? extends Enum<?>> enumType;

  EFormSw(String label, Class<? extends Enum<?>> enumType) {
    this.label = label;
    this.enumType = enumType;
  }

  public String getLabel() {
    return label;
  }

  public Class<? extends Enum<?>> getEnumType() {
    return enumType;
  }
}

When you are looping through the values of EFormSw , you can use getEnumConstants to get an Enum<?>[] representing the enum values of the enum type, but you won't be able to do much with it, because you don't know which exact enum type it is:

for (EFormSw constant: EFormSw.values()) {
    Enum<?>[] values = constant.getEnumType().getEnumConstants();
}

(You can still call most of the methods declared in java.lang.Enum and java.lang.Object on the array elements, so if that's all you need, you can just use that.)

If you want to use some common functionality shared between EObjKeyType and EObjNoteType , you can extract all the common functionality into a common interface that they both implement:

interface EObjType {
    // ...
}

enum EObjKeyType implements EObjType {
    // ...
}

enum EObjNoteType implements EObjType {
    // ...
}

Then change enumType to:

private final Class<? extends EObjType > enumType;

Now you can get a EObjType[] instead.