Faster alternatives to replace method in a Java String?

Question

The fact that the replace method returns a string object rather than replacing the contents of a given string is a little obtuse (but understandable when you know that strin

Answer 1

Adding to the @paxdiablo answer, here's a sample implementation of a replaceAll using StringBuffers that is a ~3.7 times faster than String.replaceAll():

Code:

public static String replaceAll(final String str, final String searchChars, String replaceChars)
{
  if ("".equals(str) || "".equals(searchChars) || searchChars.equals(replaceChars))
  {
    return str;
  }
  if (replaceChars == null)
  {
    replaceChars = "";
  }
  final int strLength = str.length();
  final int searchCharsLength = searchChars.length();
  StringBuilder buf = new StringBuilder(str);
  boolean modified = false;
  for (int i = 0; i < strLength; i++)
  {
    int start = buf.indexOf(searchChars, i);

    if (start == -1)
    {
      if (i == 0)
      {
        return str;
      }
      return buf.toString();
    }
    buf = buf.replace(start, start + searchCharsLength, replaceChars);
    modified = true;

  }
  if (!modified)
  {
    return str;
  }
  else
  {
    return buf.toString();
  }
}

Test Case -- the output is the following (Delta1 = 1917009502; Delta2 =7241000026):

@Test
public void testReplaceAll() 
{
  String origStr = "1234567890-1234567890-";

  String replacement1 =  StringReplacer.replaceAll(origStr, "0", "a");
  String expectedRep1 = "123456789a-123456789a-";

  String replacement2 =  StringReplacer.replaceAll(origStr, "0", "ab");
  String expectedRep2 = "123456789ab-123456789ab-";

  String replacement3 =  StringReplacer.replaceAll(origStr, "0", "");
  String expectedRep3 = "123456789-123456789-";


  String replacement4 =  StringReplacer.replaceAll(origStr, "012", "a");
  String expectedRep4 = "1234567890-1234567890-";

  String replacement5 =  StringReplacer.replaceAll(origStr, "123", "ab");
  String expectedRep5 = "ab4567890-ab4567890-";

  String replacement6 =  StringReplacer.replaceAll(origStr, "123", "abc");
  String expectedRep6 = "abc4567890-abc4567890-";

  String replacement7 =  StringReplacer.replaceAll(origStr, "123", "abcdd");
  String expectedRep7 = "abcdd4567890-abcdd4567890-";

  String replacement8 =  StringReplacer.replaceAll(origStr, "123", "");
  String expectedRep8 = "4567890-4567890-";

  String replacement9 =  StringReplacer.replaceAll(origStr, "123", "");
  String expectedRep9 = "4567890-4567890-";

  assertEquals(replacement1, expectedRep1);
  assertEquals(replacement2, expectedRep2);
  assertEquals(replacement3, expectedRep3);
  assertEquals(replacement4, expectedRep4);
  assertEquals(replacement5, expectedRep5);
  assertEquals(replacement6, expectedRep6);
  assertEquals(replacement7, expectedRep7);
  assertEquals(replacement8, expectedRep8);
  assertEquals(replacement9, expectedRep9);

  long start1 = System.nanoTime();
  for (long i = 0; i < 10000000L; i++)
  {
    String rep =  StringReplacer.replaceAll(origStr, "123", "abcdd");
  }
  long delta1 = System.nanoTime() -start1;

  long start2= System.nanoTime();

  for (long i = 0; i < 10000000L; i++)
  {
    String rep =  origStr.replaceAll( "123", "abcdd");
  }

  long delta2 = System.nanoTime() -start1;

  assertTrue(delta1 < delta2);

  System.out.printf("Delta1 = %d; Delta2 =%d", delta1, delta2);


}