Question

As far as I know, StringBuilder helps to reduce memory usage by not creating temporary string instances in the string pool during concats.
But, what happens if I do sth like this:

StringBuilder sb = new StringBuilder("bu");
sb.append("b"+"u");

Does it compile into

sb.append("b");
sb.append("u");

? Or it depends on optimalization flags? Or I loose the whole benefit if stringbuilders?
Or this quetion makes no sense? 🙂

Answer 1

It compiles to sb.append("bu"), because the compiler translates the concatenation of multiple String litterals to a single String litteral.

If you had

String a = "a";
sb.append(a + "b");

it would compile it to

String a = "a";
String temp = a + "b"; // useless creation of a string here
sb.append(temp);

So you should prefer

sb.append(a);
sb.append("b");

in this case.