Java Performance Tuning

Conversions to Strings

Generally, the JDK methods that convert objects and data types to strings are suboptimal, both in terms of performance and the number of temporary objects used in the conversion procedure. In this section, we consider how to optimize these conversions.

Converting longs to Strings

Let’s start by looking at conversion of long values. In the JDK, this is achieved with the Long.toString() method. Bear in mind that you typically add a converted value to a StringBuffer (explicitly, or implicitly with the + concatenation operator). So it would be nice to avoid the two intermediate temporary objects created while converting the long, i.e., the one char array inside the conversion method, and the returned String object that is used just to copy the chars into the StringBuffer.

Avoiding the temporary char array is difficult to do, because most fast methods for converting numbers start with the low digits in the number, and you cannot add to the StringBuffer from the low to the high digits unless you want all your numbers coming out backwards.

However, with a little work, you can get to a method that is fast and obtains the digits in order. The following code works by determining the magnitude of the number first, then successively stripping off the highest digit:

//Up to radix 36 private static final char[] charForDigit = { '0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f','g','h', 'i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z' ...