Question

I found out that Java supports constant folding of primitive types, but what about Strings?

Example

If I create the following source code

out.write(""
        + "<markup>"
        + "<nested>"
        + "Easier to read if it is split into multiple lines"
        + "</nested>"
        + "</markup>"
        + "");

What goes into the compiled code?

Combined Version? out.write("<markup><nested>Easier to read if it is split into multiple lines</nested></markup>");

Or the less efficient run-time concatenation version? out.write(new StringBuilder("").append("<markup>").append("<nested>").append("Easier to read if it is split into multiple lines").append("</nested>").append("</markup>").append(""));

Answer 1

Here’s an easy test:

public static void main(final String[] args) {
    final String a = "1" + "2";
    final String b = "12";        

    System.out.println(a == b);
}

Output:

true

So, yes, the compiler will fold.