CODEWITHSUNDEEP
javastringgenerics
Linux Geek
Linux Geek

Reputation: 967

How to convert generic type into String

I am writing a function which uses generic parameters and converts them to their specific datatype adds them and returns the added value. I have done this for integer and double, but can't do the same for the string

I have tried using toString() function as well as String constructor but nothing seems to work!

public static <T extends Number> T add(T a, T b) {
        if (a instanceof Integer) {
            return (T) Integer.valueOf(a.intValue() + b.intValue());
        } else if (a instanceof Double) {
            return (T) Double.valueOf(b.doubleValue() + b.doubleValue());
        } else if (a instanceof String) {
            return  (T) String.valueOf(a.toString() + b.toString());
        }

    }

I expect that it should return generic type argument but it throws couple of compile time errors:

java: incompatible types: T cannot be converted to java.lang.String

and 

ava: incompatible types: java.lang.String cannot be converted to T

Upvotes: 1

Views: 7819

Answers (1)

Michael Gantman
Michael Gantman

Reputation: 7792

Your Generic type T is declared to extend Number. String does not extend Number. And this is the root of your problem. Either your incoming parameters a and b extend number and thus may not be of type String or your T generic type may not extend Number.

Another solution is to have your method as it is and not deal with String type there and add another method that receives 2 String params. However, note that adding 2 strings just concatenates them, so "2" + "4" will give you "24" which is probably not what you want/expect. If you expect Strings that represent numeric values you will need to write your own code to parse your String params to Integer or Long or other implementation of Number interface and then add them up

Upvotes: 2

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