Check some members are not null

Question

I have a class with about 20 members and I have a method to validate that 10 specific members are not null. At first I thought none of them could be null so I was doing a for loop through this.getClass().getDeclaredFields() but when I learned that 10 of them could actually be null, that plan failed.

I tried googling if there was a way of setting subsets of members and looping through those only, but didn't find anything useful. Otherwise I'm left with a big if ((id == null) || (type == null) ... return false

Any ideas to do this in a cleaner way?

Answer 1

You can create an annotation to mark the fields that are not null and then just filter the list of fields according to the annotation

public class ValidateNotNullProperty
{
    public static @interface NotNull {}

    // example usage
    @NotNull
    public int id;

    public static List<Field> getMandatoryFields(Class<?> cls) {
        return Arrays.asList(cls.getDeclaredFields()).stream()
        .filter(fld -> fld.isAnnotationPresent(NotNull.class))
        .collect(Collectors.toList());
    }
}