Question

I’m about to give up on that snippet: I don’t grok Java generics… I’m trying to return the value of an enum when getting a System property with that enum name, as in:

enum E { A, B }
...
E mode = GetEnumProperty("mode", E.A);

where GetEnumProperty is:

static <T> T GetEnumProperty(String propName, T extends Enum<T> defaultValue)
{
    if (System.getProperty(propName) != null) {
        return Enum.valueOf(defaultValue.getClass(), System.getProperty(propName));
    } else {
        return defaultValue;
    }
}

Thanks!

Answer 1

It looks like what you want is this:

public class GenericEnum {
    static <T extends  Enum<T>> T GetEnumProperty(String propName, T defaultValue)
    {
        if (System.getProperty(propName) != null) {
            return (T)Enum.valueOf(defaultValue.getClass(), System.getProperty(propName));
        } else {
            return defaultValue;
        }
    }

Notice the change in how generic type T is specified in the method declaration. You need to declare that the type T extends Enum before you use it in the parameter list.

Also note the cast (T) in the first return statement.