How to check if a String contains another String in a case insensitive manner in Java?

Question

Say I have two strings,

String s1 = \"AbBaCca\";
String s2 = \"bac\";

I want to perform a check returning that s2 is contained

Answer 1

I did a test finding a case-insensitive match of a string. I have a Vector of 150,000 objects all with a String as one field and wanted to find the subset which matched a string. I tried three methods:

1. Convert all to lower case

   for (SongInformation song: songs) {
       if (song.artist.toLowerCase().indexOf(pattern.toLowercase() > -1) {
               ...
       }
   }
   

2. Use the String matches() method

   for (SongInformation song: songs) {
       if (song.artist.matches("(?i).*" + pattern + ".*")) {
       ...
       }
   }
   

3. Use regular expressions

   Pattern p = Pattern.compile(pattern, Pattern.CASE_INSENSITIVE);
   Matcher m = p.matcher("");
   for (SongInformation song: songs) {
       m.reset(song.artist);
       if (m.find()) {
       ...
       }
   }
   

Timing results are:

• No attempted match: 20 msecs

• To lower match: 182 msecs

• String matches: 278 msecs

• Regular expression: 65 msecs

The regular expression looks to be the fastest for this use case.