How to check if a given string is a part of any given Enum in Java?

Question

I have two different enums and i want to be able to output whether a given string is a part of a enum collection. this is my code:

public class Check {
    public enum Filter{SIZE, DATE, NAME};
    public enum Action{COPY, DELETE, REMOVE};

    public boolean isInEnum(String value, Enum e){
        // check if string value is a part of a given enum
        return false;
    }

    public void main(){
        String filter = "SIZE";
        String action = "DELETE";
                // check the strings
        isInEnum(filter, Filter);
        isInEnum(action, Action);
    }
}

eclipse says that in the last two lines "Filter can't be resolved to a variable" but apart from that it seems that the Enum param in the function "isInEnum" is wrong.

Something is very wrong here can anyone help?

Answer 1

The simplest (and usually most efficient) way is as follows:

public <E extends Enum<E>> boolean isInEnum(String value, Class<E> enumClass) {
  for (E e : enumClass.getEnumConstants()) {
    if(e.name().equals(value)) { return true; }
  }
  return false;
}

and then you call isInEnum(filter, Filter.class) .

Answer 2

If you don't mind using Apache commons lang3 library you can use the following code:

EnumUtils.isValidEnum(Filter.class, filter)

According to the docs :

This method differs from Enum.valueOf(java.lang.Class, java.lang.String) in that it does not throw an exception for an invalid enum name.

Answer 3

Here is a Java 8/streams version of Louis Wasserman's answer. (You can also put this method directly into the Enum class, and remove one of the parameters)

public boolean isInEnum(String value, Class<E> enumClass) {
    return Arrays.stream(enumClass.getEnumConstants()).anyMatch(e -> e.name().equals(value));
  }

Answer 4

I don't have enough points to comment on Simon Tower's answer directly, but here is the method for the second way he mentioned that goes directly in the enum class itself:

 public static boolean isInEnum(String value) {
     return Arrays.stream(EnumClassNameGoesHere.values()).anyMatch(e -> e.name().equals(value));
}

Answer 5

Avoid using a loop to do the validation.

I would suggest using valueOf . This method is built-in to enums, and might be considered for compile time optimization.

This would be like similar to implementing a static Map<String,EnumType> to optimize the lookup, an other consideration you can take.

Drawback is that you would have to use the exception handling mechanism to catch a non-enum value.

Example

public enum DataType {
  //...
  static public boolean has(String value) {
    if (value== null) return false;
    try { 
        // In this implementation - I want to ignore the case
        // if you want otherwise ... remove .toUpperCase()
        return valueOf(value.toUpperCase()); 
    } catch (IllegalArgumentException x) { 
        // the uggly part ...
        return false;
    }
  }
}

Also note that with above type implementation, your code looks much cleaner when calling. Your main would now look something like:

public void main(){
    String filter = "SIZE";
    String action = "DELETE";

    // ...

    if (Filter.has(filter) && Action.has(action)) {
      // Appropriate action
    }
}

Then the other mentioned option is to use a static Map. You can employ such an approach to cache all sort of indexing based on other properties too. In below example, I allow each enum value to have a list of alias names. The lookup index in this case will be case insensitive, by forcing to uppercase.

public enum Command {
  DELETE("del","rm","remove"),
  COPY("cp"),
  DIR("ls");

  private static final Map<String,Command> ALIAS_MAP = new HashMap<String,Command>();
  static {
    for (Command type:Command.values()) {
      ALIAS_MAP.put(type.getKey().toUpper(),type);
      for (String alias:type.aliases) ALIAS_MAP.put(alias.toUpper(),type);
    }
  }

  static public boolean has(String value) {
    return ALIAS_MAP.containsKey(value.toUpper());
  }

  static public Command fromString(String value) {
    if (value == null) throw new NullPointerException("alias null");
    Command command = ALIAS_MAP.get(value);
    if (command == null) throw new IllegalArgumentException("Not an alias: "+value);
    return command;
  }

  private List<String> aliases;
  private Command(String... aliases) {
    this.aliases = Arrays.asList(aliases);
  }
}