Search for a word in a String

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.

Answer 2

Method one should be faster because it has lesser overhead. if it is about performance in searching in huge files a specialized method like boyer moore pattern matching could lead to further improvements.

Answer 3

If you are looking for a fixed string, not a pattern, as in the example in your question, indexOf will be better (simpler) and faster, since it does not need to use regular expressions.

Also, if the string you are searching for does contain characters that have a special meaning in regular expressions, with indexOf you don't need to worry about escaping these characters.

In general, use indexOf where possible, and match for pattern matching, where indexOf cannot do what you need.