indexOf does a case sensitive compare. It comes is several versions. The ones that search for single characters are faster than the ones that search for Strings.

For long string searches, consider using the Boyer Moore algorithm, or searching for an obscure character first, then checking the candidate for a full match.

Gotchas

// This code returns 6:
// the index relative to the start of the origingal String,
// not relative to the substring searched starting at offset 2
System.out.println( "deccccdefgh".indexOf( "de", 2 ) );