split based on uppercase in java [duplicate]

Question

Anyone know how to do how to covert FirstName to First Name.

The splitting has to take place based on The Upper-Case letters , but it should exclude the first letter.

I know how to do it using split. There is any other way to do it apart from split functionality.

Answer 1

Not really split, just replaceAll:

str.replaceAll("(?!^)([A-Z])", " $1")

This solution assumes that you don't want to add space before an uppercase English alphabet if it is the first character in the string. So, " FirstName" will become "  First Name" (note the 2 spaces).

(?!^) is negative look-ahead (?!pattern), just checking this is not the beginning of the string ^. I capture (pattern) the uppercase English alphabet, and use the captured text in the replacement $1 ($1 means whatever captured in capturing group 1 is put in the replacement string - in this case there is only 1 capturing group).

Another solution that add space before an uppercase English alphabet, only if it is preceded by lowercase English alphabet:

str.replaceAll("(?<=[a-z])([A-Z])", " $1")

(?<=[a-z]) is a positive look-behind (?<=pattern) that checks whether the capital characters [A-Z] is preceded by lowercase English alphabet [a-z]. The rest has been explained above.

The pattern can vary a lot based on the requirement. You only give one example instead of concrete requirement, so I will take a wild guess and pick out a pattern for you.

Answer 2

6 to 11 times faster than replaceAll :

  StringBuilder s = new StringBuilder( "FirstName" );
  for( int i = 1; i < s.length(); ++i ) {
     if( Character.isUpperCase( s.charAt( i ))) {
        s.insert( i++, ' ' );
     }
  }

bench :

  long atStart = System.currentTimeMillis();
  for( int j = 0; j < 1000000; ++j ) {
     StringBuilder s = new StringBuilder( "FirstName" );
     for( int i = 1; i < s.length(); ++i ) {
        if( Character.isUpperCase( s.charAt( i ))) {
           s.insert( i++, ' ' );
        }
     }
  }
  long elapsed1 = System.currentTimeMillis() - atStart;

  atStart = System.currentTimeMillis();
  for( int j = 0; j < 1000000; ++j ) {
     String s = "FirstName";
     s = s.replaceAll("(?!^)([A-Z])", " $1");
  }
  long elapsed2 = System.currentTimeMillis() - atStart;

  System.err.println( "Ratio: " + elapsed2 / (double)elapsed1 );