A common pattern in Java is to declare an enum, and then use Set to declare subsets of the enum.  The subsets can then be used to validate that they contain a value passed as the enum type.  

For instance:

  public enum Command {INSERTNEW, DELETEOTHERS, CREATERANDOMCONTACTS}

// Define commands that only require the AccountNumber to operate
public static Set<MyClass.Command> accountNumberOnlyCommands;

static {
accountNumberOnlyCommands.add(Command.DELETEOTHERS);
accountNumberOnlyCommands.add(Command.CREATERANDOMCONTACTS);
}

would allow you to then do:

public MyClass(Command thisCommand) {
if (accountNumberOnlyCommands.contains( thisCommand ) )

...

But, when you try to declare your Set<enum type>, it creates a build error of "Set of <enum type> not allowed".  Why would it not allow this?  After all, an enum, besides being a type declaration, is conceptual a set of unique values. It is only logical to be able to use Set to declare subsets and then the contains method to verify that a value is a member of the subset.  And, like I said, you can do this in Java. 

If you change Set to List in the declaration, it allows it, so you can create lists of an enum type.  But, List doesn't have the contains method, so it then errors on the if statement above.  

Does anyone know how to resolve this?