Strings, Characters and Regular Expressions - Java: How to Program Early Objects - page 614

Performance Tip 14.5
Dynamically increasing the capacity of a StringBuilder can take a relatively long time.
Executing a large number of these operations can degrade the performance of an applica-
tion. If a StringBuilder is going to increase greatly in size, possibly multiple times, setting
its capacity high at the beginning will increase performance.

Line 16 uses method setLength to set the length of the StringBuilder to 10. If the
specified length is less than the current number of characters in the StringBuilder , its
contents are truncated to the specified length (i.e., the characters in the StringBuilder
after the specified length are discarded). If the specified length is greater than the number
of characters currently in the StringBuilder , null characters (characters with the
numeric representation 0) are appended until the total number of characters in the
StringBuilder is equal to the specified length.

14.4.3 StringBuilder Methods charAt , setCharAt , getChars and
reverse
Class StringBuilder provides methods charAt , setCharAt , getChars and reverse to ma-
nipulate the characters in a StringBuilder (Fig. 14.12). Method charAt (line 12) takes an
integer argument and returns the character in the StringBuilder at that index. Method
getChars (line 15) copies characters from a StringBuilder into the character array passed
as an argument. This method takes four arguments—the starting index from which charac-
ters should be copied in the StringBuilder , the index one past the last character to be copied
from the StringBuilder , the character array into which the characters are to be copied and
the starting location in the character array where the first character should be placed. Method
setCharAt (lines 21 and 22) takes an integer and a character argument and sets the character
at the specified position in the StringBuilder to the character argument. Method reverse
(line 25) reverses the contents of the StringBuilder . Attempting to access a character that's
outside the bounds of a StringBuilder results in a StringIndexOutOfBoundsException .

1 // Fig. 14.12: StringBuilderChars.java

2 // StringBuilder methods charAt, setCharAt, getChars and reverse.

3
4 public class StringBuilderChars

5 {

6 public static void main(String[] args)

7 {

8 StringBuilder buffer = new StringBuilder( "hello there" );

9
10 System.out.printf( "buffer = %s%n" , buffer.toString());

11 System.out.printf( "Character at 0: %s%nCharacter at 4: %s%n%n" ,

12 buffer.charAt( 0 ) buffer.charAt( 4 ) , );

13
14 char [] charArray = new char[buffer.length()];

15 buffer.getChars( 0 , buffer.length(), charArray, 0 );

16 System.out.print( "The characters are: " );

Fig. 14.12 | StringBuilder methods charAt , setCharAt , getChars and reverse . (Part 1
of 2.)