I'm facing a dilemma. I'm parsing a string and can either do
s.matches(regex)
or I can do
s.startsWith(..) && s.endsWith(..)
As you already realize, its not a complicated regexp, and both situations will work. The idea is, the string may be very long (hundreds of chars), so I wish to maximize efficiency. What works how and better suits the issue?
Here's a really rather crude benchmark to give you an idea. Adapt it to your use cases to give you more relevant results.
startsWith() and endsWith() are much fasterResults after 1 000 000 runs:
- Uncompiled pattern: 1091 ms - Compiled pattern: 745 ms - startsWith() / endsWith(): 24 ms
public class TestRegex {
String regex = "^start.*end$";
Pattern p = Pattern.compile(regex);
String start = "start";
String end = "end";
String search = start + "fewbjlhfgljghfadsjhfdsaglfdhjgahfgfjkhgfdkhjsagafdskghjafdkhjgfadskhjgfdsakhjgfdaskhjgafdskjhgafdsjhkgfads" + end;
int runs = 1000000;
@Test
public final void test() {
// Init run
for (int i = 0; i < runs; i++) {
search.matches(regex);
}
for (int i = 0; i < runs; i++) {
p.matcher(search).matches();
}
for (int i = 0; i < runs; i++) {
search.startsWith(start);
search.endsWith(end);
}
// Timed run
Stopwatch s = Stopwatch.createStarted();
for (int i = 0; i < runs; i++) {
search.matches(regex);
}
System.out.println(s.elapsed(TimeUnit.MILLISECONDS));
s.reset();
s.start();
for (int i = 0; i < runs; i++) {
p.matcher(search).matches();
}
System.out.println(s.elapsed(TimeUnit.MILLISECONDS));
s.reset();
s.start();
for (int i = 0; i < runs; i++) {
search.startsWith(start);
search.endsWith(end);
}
System.out.println(s.elapsed(TimeUnit.MILLISECONDS));
}
}
Note that both methods may report different results in cases where the string expeted at the end is a suffix of the start string:
^start.*art$
will not match
"start"
while
"start".startsWith("start") && "start".endsWith("art")
will be true.
Indeed, the difference is there and noticeable for small strings as well. Having a compiled version of the regex using a pattern does make some enhancements, but no doubt, its the worst idea when the match is easy.
Thanks everyone.
