different implementations of string reverse in Java

reverse

public String reverse(String str) {
  if(str == null)
    throw new NullPointerException("null");
  if(str.length() <= 1)
    return str;
    
  return new StringBuffer(str).reverse().toString();
}

public String reverseTwo(String str) {
  if(str == null)
    throw new NullPointerException("null");
  if(str.length() <= 1)
    return str;
    
  return reverseTwo(str.subString(1)) + str.chartAt(0);
}

public String reverseThree(String str) {
  if(str == null)
    throw new NullPointerException("null");
  if(str.length() <= 1)
    return str;
    
  StringBuffer sb = new StringBuffer(str.length());
  for(int i = str.length() - 1; i >= 0; i--) {
    sb.append(str.chartAt(i));
  }
  
  return sb.toString();
}
//Also another implementations...
public String reverseFour(char[] value) {
  if(value == null)
    throw new NullPointerException("null");
  if(value.length == 1)
    return new String(value);
    
  for(int i = (value.length - 1) >>1; i >= 0; i--) {
    char temp = value[i];
    value[i] = value[value.length - 1 - i];
    value[value.length - 1 - i] = temp;
  }
  
  return new String(value);
}