Strings and Things - Java - page 89

Discussion

An object of one of the StringBuilder classes basically represents a collection of charac-
ters. It is similar to a String object, but, as mentioned, String s are immutable.
StringBuilder s are mutable and designed for, well, building String s. You typically con-
struct a StringBuilder , invoke the methods needed to get the character sequence just the
way you want it, and then call toString() to generate a String representing the same char-
acter sequence for use in most of the Java API, which deals in String s.

StringBuffer is historical—it's been around since the beginning of time. Some of its meth-
ods are synchronized (see Synchronizing Threads with the synchronized Keyword ), which
involves unneeded overhead in a single-threaded context. In Java 5, this class was “split” in-
to StringBuffer (which is synchronized) and StringBuilder (which is not synchronized);
thus, it is faster and preferable for single-threaded use. Another new class, Ab-
stractStringBuilder , is the parent of both. In the following discussion, I'll use “the
StringBuilder classes” to refer to all three because they mostly have the same methods.

The topic's example code provides a StringBuilderDemo and a StringBufferDemo . Except
for the fact that StringBuilder is not threadsafe, these API classes are identical and can be
used interchangeably, so my two demo programs are almost identical except that each one
uses the appropriate builder class.

The StringBuilder classes have a variety of methods for inserting, replacing, and otherwise
modifying a given StringBuilder . Conveniently, the append() methods return a reference
to the StringBuilder itself, so statements like .append(…).append(…) are fairly common.
You might even see this third way in a toString() method. Example 3-2 shows three ways
of concatenating strings.

Example 3-2. StringBuilderDemo.java
public public class class StringBuilderDemo StringBuilderDemo {

public public static static void void main ( String [] argv ) {

String s1 = "Hello" + ", " + "World" ;
System . out . println ( s1 );

// Build a StringBuilder, and append some things to it.
StringBuilder sb2 = new

new StringBuilder ();

sb2 . append ( "Hello" );
sb2 . append ( ',' );
sb2 . append ( ' ' );