Question

i would like to get rid of these warnings about unchecked conversion and parameterization without surpressing them.

interface Switch {
    void toggle();
}
enum A implements Switch {
    a1,a2;
    @Override public void toggle() {
        state=!state;
    }
    boolean state;
}
enum B implements Switch {
    b1,b2;
    @Override public void toggle() {
        state=!state;
    }
    boolean state;
}
public class Warnings {
    public static void main(String[] args) {
        Class<? extends Enum>[] enums=new Class[]{A.class,B.class};
        for(Class<? extends Enum> clazz:enums)
            try {
                Enum s=Enum.valueOf(clazz,args[0]);
                ((Switch)s).toggle();
            } catch(IllegalArgumentException eee) {}
    }
}

Answer 1

You can’t without writing your own valueOf. Enum is defined as:

class Enum<E extends Enum<E>>

and Enum.valueOf is defined as:

public static <T extends Enum<T>> T valueOf(Class<T> enumType,
                                            String name) 

Note the recursive type parameterization which implies that you can only call valueOf with a specific enum class (e.g. A.class), but not with a generic one, as a Class<? extends Enum<?>> is not a match because the two question marks aren’t assumed to represent the same (unknown) type by the compiler.

So apart from using generic collections instead of arrays, you have to write your own valueOf method that accepts any enum class.

public class Warnings {
    public static void main(final String[] args) {
        List<Class<? extends Enum<?>>> enums = new ArrayList<Class<? extends Enum<?>>>();
        enums.add(A.class);
        enums.add(B.class);
        for (Class<? extends Enum<?>> clazz : enums) {
            try {
                Switch s = valueOf(clazz, args[0]);
                s.toggle();
            } catch (IllegalArgumentException eee) {
            }
        }
    }

    private static Switch valueOf(final Class<? extends Enum<?>> enumClass, final String name) {
        Enum<?>[] enumConstants = enumClass.getEnumConstants();
        for (Enum<?> constant : enumConstants) {
            if (constant.name().equals(name)) {
                return (Switch) constant;
            }
        }
        throw new IllegalArgumentException(name + " is not a constant of enum class " + enumClass.getName());
    }
}