StringBuilder append vs +

Question

What is the difference between these two lines?

stringBuilder.append("Text " + counter + " more text");
stringBuilder.append("Text ").append(counter).append(" more text");

Assuming that counter is an incrementing int, does the first line create a String "Text 0 more text", "Text 1 more text", etc. each time it's called, while the second line creates only these two Strings once: "Text " and " more text"? Is this correct?

Answer 1

In a nutshell, yes, except that the same string literals for "Text " and " more text" get reused every time.

The second variant is more efficient, since it writes each of the three components directly into the StringBuilder.

In contrast, the first variant creates another -- unnamed -- StringBuilder, writes the three components into it, calls its toString() method and writes the result into the named stringBuilder.

In summary, the first variant creates an extra StringBuilder object and an extra String object, and copies the string data twice more than the second variant.