Is concatenating with an empty string to do a string conversion really that bad?

Question

Let's say I have two char variables, and later on I want to concatenate them into a string. This is how I would do it:

char c1, c2; // ...  String s = "" + c1 + c2; 

I've seen people who say that the "" + "trick" is "ugly", etc, and that you should use String.valueOf or Character.toString instead. I prefer this construct because:

• I prefer using language feature instead of API call if possible
  • In general, isn't the language usually more stable than the API?
  • If language feature only hides API call, then even stronger reason to prefer it!
    • More abstract! Hiding is good!
• I like that the c1 and c2 are visually on the same level
  • String.valueOf(c1) + c2 suggests something is special about c1
• It's shorter.

Is there really a good argument why String.valueOf or Character.toString is preferrable to "" +?

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Trivia: in java.lang.AssertionError, the following line appears 7 times, each with a different type:

    this("" + detailMessage); 

Answer 1

Your arguments are good; this is one of the more expressive areas of the Java language, and the "" + idiom seems well entrenched, as you discovered.

See String concatenation in the JLS. An expression like

"" + c1 + c2 

is equivalent to

new StringBuffer().append(new Character(c1).toString())                   .append(new Character(c2).toString()).toString() 

except that all of the intermediate objects are not necessary (so efficiency is not a motive). The spec says that an implementation can use the StringBuffer or not. Since this feature is built into the language, I see no reason to use the more verbose form, especially in an already verbose language.

Answer 2

The problem with that construct is that it usually doesn't express the intent.

It represents concatenation of a String with another value, but concatenation is not usually the goal of this line.

In the specific case that you demonstrated, concatenation is actually the goal, so this code does express the intent.

In the more common use of this approach (String s = "" + intValue;), the concatentation is merely a tolerated side-effect, while the conversion of intValue is the actual goal. And a simple String.valueOf(intValue) expresses that intent much clearer.