Including "+" sign in Enum

[B Nirvan]

Hi,
I have an enum that represents blood group. Allowable values are (A+, A- , B+, B-, AB+, AB-, O+, O-). The problem is that I am not able to define the enum because of the special character "+". I tried to escape it using A\+, but that doesn't work. Also tried to put the values in quotes (single and double) and that doesn't work too. How should I define enums for these blood groups.

regards,
Nirvan.

[Rob Spoor]

Give them other names, with a String field for the label:

public enum BloodType
{
    A_POSITIVE("A+"),
    A_NEGATIVE("A-"),
    ...
    O_NEGATIVE("O-");

    private final String label;

    private BloodType(String label) { this.label = label; }

    @Override
    public String toString() { return label; }
}

If needed you can add a static method that returns a blood type for a specific label; loop over the values() until you find one with the label. Return null or throw an exception if none is found.

[David O'Meara]

You could maintain a HashMap<String, BloodType> for the reverse reference if you get stressed but I usually find it isn't worth the effort and pretty much do as Rob says.

[Campbell Ritchie]

Nobody working with blood ever writes A+ or A-. They only write Apos or Aneg.

[B Nirvan]

Rob,
Your solution seems to be nice and simple. I will use it.

Campbell,
My client wants to search the donors based on the blood group. I think it is much simpler to select from a dropdown list of blood groups using A+ format rather than Apos. But I am welcome for any drawbacks in using the earlier.

regards,
Nirvan.

[Wouter Oet]

So you are changing your model because the view wants that? So if the client decides that it wants yet another format you're going to change your model? I would separate the concerns using something like MVC.

[B Nirvan]

Am I changing the model ? I don't think so. I will be storing integer values for the model. I believe that I am be only changing the view. If client needs a different format, I don't have to change the values in the database. Just changing the Enum strings ("A+") to (Apos) will work. Or there is something that I am failing to comprehend.

regards,
Nirvan.

[Matthew Brown]

If you're using integers in the database to represent these values, I'd suggest having a lookup table in the database mapping the integers to the descriptions.

As things stand if you were asked to change from A+ to A-positive, you'd have to recompile your code and deploy a new version. As opposed to just changing a single value in the database.

[B Nirvan]

Matthew,
I agree with your suggestion. But I don't think the client will ask for a change in the display type of the blood groups. Still I will think about using database look up of the integer values.

Thanks very much to all of you.

regards,
Nirvan.

[Daniel Sagayaraj]

public enum Temp {
        A(1,1),
        B(1,1),
        AB(1,1),
        O(1,1);
        
        

    private final int positive;
    private final int negative;
    private final char plus='+';
    private final char minus='-';
    
    Temp(int positive, int negative) {
        this.positive = positive;
        this.negative = negative;
    }
    public String positive()   
    {
        if(positive==1)
        {
    	String name=name();
		return name+plus;
        }else
        {
        	return  null;
        }
    }
    public String negative()   
    {
        if(negative==1)
        {
    	String name=name();
		return name+minus;
        }else
        {
        	return  null;
        }
    }
    



   
    public static void main(String[] args) {
        
        
        for (Temp p : Temp.values())
        {
           System.out.println(p.positive());
        System.out.println(p.negative());
        }
    }
}

==============


OutPut::

A+
A-
B+
B-
AB+
AB-
O+
O-



=========================


With this we can achieve the expected task in your project

[Rob Spoor]

Please UseCodeTags next time. I've added them this time.

Two comments:
- surely you are not using int where boolean should be used? Both positive and negative should be booleans of course!
- your example now requires if statements within the loop to generate the entire list of blood types. That adds complexity.

[Campbell Ritchie]

The reason for writing Apos rather than A+ is to avoid confusion and possible mis-readings, which with blood groups might be fatal.

[Wouter Oet]

Nirvan Buddha wrote:Am I changing the model ? I don't think so. I will be storing integer values for the model. I believe that I am be only changing the view. If client needs a different format, I don't have to change the values in the database. Just changing the Enum strings ("A+") to (Apos) will work. Or there is something that I am failing to comprehend.

regards,
Nirvan.

I would extract the information from the model. An example where your model fails: Client 1 want A+ Client 2 wants Apos. Or what if he wants it in 2 different languages (not that A+ would be different in another language but you get the point).