Question

If I am looking for a particular word inside a string, for example, in the string “how are you” I am looking for “are”.
Would a regular indexOf() work faster and better or a Regex match()

String testStr = "how are you";
String lookUp = "are";

//METHOD1
if (testStr.indexOf(lookUp) != -1)
{
 System.out.println("Found!");
}

//OR
//METHOD 2
if (testStr.match(".*"+lookUp+".*"))
{
 System.out.println("Found!");
}

Which of the two methods above is a better way of looking for a string inside another string? Or is there a much better alternative?

• Ivard

Answer 1

If you don’t care whether it’s actually the entire word you’re matching, then indexOf() will be a lot faster.

If, on the other hand, you need to be able to differentiate between are, harebrained, aren't etc., then you need a regex: \bare\b will only match are as an entire word (\\bare\\b in Java).

\b is a word boundary anchor, and it matches the empty space between an alphanumeric character (letter, digit, or underscore) and a non-alphanumeric character.

Caveat: This also means that if your search term isn’t actually a word (let’s say you’re looking for ###), then these word boundary anchors will only match in a string like aaa###zzz, but not in +++###+++.

Further caveat: Java has by default a limited worldview on what constitutes an alphanumeric character. Only ASCII letters/digits (plus the underscore) count here, so word boundary anchors will fail on words like élève, relevé or ärgern. Read more about this (and how to solve this problem) here.