Convert null to Enum.NULL

Question

I have an enum like this:

public enum Type{
    CSV, EXCEL, PDF, URL, NULL
}

now I am reading a line from an xml file and use the Type.valueOf(string);parsing values ​​to parse. if this part does not exist in the xml file, string null, not "null". Is there a way to convert nullto "null"or change return null;to return "null";? or should not even be included in the listing?

Answer 1

What you need to do is use something else than NULL, and analyze this case differently:

public enum Type {
  CSV, EXCEL, PDF, URL, NONE;
  public static Type from(String text) {
    if (text == null) {
      return NONE;
    } else {
      return valueOf(text.toUpperCase());
    }
  }
}

Or better yet, use the options:

public enum Type {
  CSV, EXCEL, PDF, URL; // Note the absence of NULL/NONE/WHATEVER
  public static Optional<Type> from(String text) {
    return Optional.ofNullable(text)
      .map(String::toUpperCase)
      .map(Type::valueOf);
  }
}

Answer 2

Type.valueOf(null), NullPointerException. :

• , null:

  public static Type getType(String name) {
      if (name == null)
          return Type.NULL;
      else
          return Type.valueOf(name.toUpperCase());
  }
  

• ( null) :

  public enum Type {
      CSV, EXCEL, PDF, URL, NULL;
  
      private static final Map<String, Type> TYPE_BY_NAME = new HashMap<>();
      static {
          TYPE_BY_NAME.put(CSV.name(), CSV);
          TYPE_BY_NAME.put(EXCEL.name(), EXCEL);
          TYPE_BY_NAME.put(PDF.name(), PDF);
          TYPE_BY_NAME.put(URL.name(), URL);
          TYPE_BY_NAME.put(null, NULL);
      }
  
      public static Type getType(String name) {
          String s = name == null ? null : name.toUpperCase();
          return TYPE_BY_NAME.get(s);
      }
  

, , . , , .