Question

The following Jsoup code concatenates the text of all elements in container els:

for (Element el : els)
  entireText += el.text();          

On a container with ~64 elements, each containing ~1KB (totaling in entireText being ~64KB), this simple loop takes about 8 seconds on a typical low-end Android phone.

This slow performance kind of surprises me because I was under the impression that Java compilers substitute expressions like A + B + C with new StringBuilder(A).append(B).append(C).toString().

Is that not the case?

What am I missing?

Answer 1

This slow performance kind of surprises me because I was under the
impression that Java compilers substitute expressions like A + B + C
with new StringBuilder(A).append(B).append(C).toString().

And so the compiler creates the code:

for (Element el : els)
  entireText = new StringBuilder(entireText).append(el.text()).toString(); 

You will need to create the StringBuilder outside the loop and append to it manually.