The @FieldNameConstants annotation generates an inner type which contains 1 constant for each field in your class. The two following are equivalent

import lombok.experimental.FieldNameConstants;
import lombok.AccessLevel;

@FieldNameConstants
public class FieldNameConstantsExample {
  private final String iAmAField;
  private final int andSoAmI;
  @FieldNameConstants.Exclude private final int asAmI;
}

public class FieldNameConstantsExample2 {
  private final String iAmAField;
  private final int andSoAmI;
  private final int asAmI;
  
  public static final class Fields {
    public static final String iAmAField = "iAmAField";
    public static final String andSoAmI = "andSoAmI";
  }
}

How does Lombok achieve that ? I wanted to make my own annotation on each fields where the inner class Fields’ constants are customized (basically @FieldNameConstants(value = “XXX” on each field), but while I understand how to make custom annotations for each field in Java, it seems a far cry from what Lombok does.