When to use StringBuilder in Java [duplicate]

Answer 1

Some compilers may not replace any string concatenations with StringBuilder equivalents. Be sure to consider which compilers your source will use before relying on compile time optimizations.

Answer 2

Have a look at: http://www.javaspecialists.eu/archive/Issue068.html and http://www.javaspecialists.eu/archive/Issue105.html

Do the same tests in your environment and check if newer JDK or your Java implementation do some type of string operation better with String or better with StringBuilder.

Answer 3

The Microsoft certification material addresses this same question. In the .NET world, the overhead for the StringBuilder object makes a simple concatenation of 2 String objects more efficient. I would assume a similar answer for Java strings.

Answer 4

If you use String concatenation in a loop, something like this,

String s = "";
for (int i = 0; i < 100; i++) {
    s += ", " + i;
}

then you should use a StringBuilder (not StringBuffer) instead of a String, because it is much faster and consumes less memory.

If you have a single statement,

String s = "1, " + "2, " + "3, " + "4, " ...;

then you can use Strings, because the compiler will use StringBuilder automatically.

Answer 5

As a general rule, always use the more readable code and only refactor if performance is an issue. In this specific case, most recent JDK's will actually optimize the code into the StringBuilder version in any case.

You usually only really need to do it manually if you are doing string concatenation in a loop or in some complex code that the compiler can't easily optimize.

Answer 6

For two strings concat is faster, in other cases StringBuilder is a better choice, see my explanation in concatenation operator (+) vs concat()