Creating List of Enums?

Question

So I have three enums and I want to make an ArrayList out of them. Here's my code:

enum Outlook {
    SUNNY, RAINY, CLOUDY
}
enum Temperature {
    HOT, COLD, MILD
}
enum Humidity {
    HIGH, NORMAL, LOW
}

And I want my ArrayList to look something like:

{Outlook, Temperature, Humidity}

Here's what I've tried:

ArrayList<Enum> attributes = new ArrayList<Enum>();
attributes.add(Temperature);

But already Eclipse tells me "Temperature cannot be resolved to a variable". Any idea how to achieve what I'm aiming for here?

Answer 1

I'm surmising that you want the names of the enums themselves, and not their values. As such, try the following code:

public static void main (String[] args) throws java.lang.Exception
{
    List<Class<? extends Enum>> myEnums = new ArrayList<>();
    myEnums.add(Outlook.class);
    myEnums.add(Temperature.class);
    myEnums.add(Humidity.class);
    System.out.println(myEnums);
}

enum Outlook {
    SUNNY, RAINY, CLOUDY
}
enum Temperature {
    HOT, COLD, MILD
}
enum Humidity {
    HIGH, NORMAL, LOW
}

You can see the demo here which will output:

[class Ideone$Outlook, class Ideone$Temperature, class Ideone$Humidity]

If you strictly need something like:

[Outlook, Temperature, Humidity]

and just can't like the extra class Ideone$... info then we can add some extra sophistication.

Answer 2

I want to loop through all of the classes (Outlook, Temp, Humidity) and, for each of them, calculate information gain. This is a function that makes use of each possible value of a given attribute (Outlook, Temp, Humidity).

One possibility would be to define a common interface implemented by all the attributes. This would allow your information-gain function to use the same interface regardless of attribute. And no reflection is required. For example:

interface IAttribute {
    Enum<?>[] getValues();
    String getName();
}

This interface applies to attribute classes as a whole, and not a particular attribute value. Here's one way to do that.

private static final class OutlookAttribute implements IAttribute {
    enum Outlook { SUNNY, RAINY, CLOUDY }

    @Override
    public Outlook[] getValues() { return Outlook.values(); }

    @Override
    public String getName() { return "Outlook"; }
}

// And similarly for Temperature and Humidity

Now you can create a list of attributes to pass to your function.

List<IAttribute> attributes = new ArrayList<>();
attributes.add( new OutlookAttribute() );
attributes.add( new TemperatureAttribute() );
attributes.add( new HumidityAttribute() );

And your function definition can iterate through attributes.

for ( IAttribute attribute : attributes ) {
   Object[] values = attribute.getValues();
   ...
   for ( Object value : values ) {
      ...
   }
   ...
}