How to concat these Strings effectively in Java 8?

Question

I need a string as follows.

s = "$.vars.start.params.operations.values"

I've tried to write it like this:

String s = "$".concat(".").concat("start").concat(".").concat("params").concat(".").
concat("operations").concat(".").concat("values");

There's a chain of concat operations.

Is there a better way of doing this?

• luk2302: "$" + "..." + "..."!? Or just have the plain string since there is nothing dynamic in the string anyway. Or join
• IS4: What's wrong with "$." + start + "." + params + ... (assuming those are actually variables)?

Answer 1

Never ever use concat like this. It is bound to be less efficient than the code the compiler generates when using +. Even worse, the code as shown (using only String literals) would have been replaced with a single string literal at compile time if you had been using + instead of concat. There is almost never a good reason to use concat (I don't believe I have ever used it, but maybe it could be useful as a method reference in a reduce operation).

In general, unless you are concatenating in a loop, simply using + will get you the most (or at least relatively good) performant code. When you do have a loop, consider using a StringBuilder.

Answer 2

It seems like you're looking for Java 8 method String.join(delimiter,elements), which expects a delimiter of type CharSequence as the first argument and varargs of CharSequence elements.

String s = String.join(".", "$", "vars", "start", "params", "operations", "values");

Answer 3

Do you have a reason for using .concat? In this case, you would approach this by using something like "$"+"..." etc.

If you wanted to add a dynamic approach, I would recommend using variables instead. It would look like

String s = variable1 + variable2 + variable; 

If you are looking for something a bit more than there is also the String.join