Arrays and Strings - Beginning Java 2 SDK - page 154

This will copy characters from text at index positions 9 to 11 inclusive, so textArray[0] will be ' n ',
textArray[1] will be ' o ', and textArray[2] will be ' t '.
You can also extract characters into a byte array using the getBytes() method in the class String .
This converts the original string characters into the character encoding used by the underlying
operating system - which is usually ASCII. For example:
String text = "To be or not to be"; // Define a string
byte[] textArray = text.getBytes(); // Get equivalent byte array
The byte array textArray will contain the same characters as in the String object, but stored as 8-
bit characters. The conversion of characters from Unicode to 8-bit bytes will be in accordance with the
default encoding for your system. This will typically mean that the upper byte of the Unicode character
is discarded resulting in the ASCII equivalent.
Creating String Objects from Character Arrays
The String class also has a static method, copyValueOf() , to create a String object from an array of
type char[] . You will recall that a static method of a class can be used even if no objects of the class exist.
Suppose you have an array defined as:
char[] textArray = {'T', 'o', ' ', 'b', 'e', ' ', 'o', 'r', ' ',
'n', 'o', 't', ' ', 't', 'o', ' ', 'b', 'e' };
You can then create a String object with the statement:
String text = String.copyValueOf(textArray);
This will result in the object text referencing the string To be or not to be .
Another version of the copyValueOf() method can create a string from a subset of the array
elements. It requires two additional arguments to specify the index of the first character in the array to
be extracted and the count of the number of characters to be extracted. With the array defined as
previously, the statement:
String text = String.copyValueOf(textArray, 9, 3);
extracts three characters starting with textArray[9] , so text will contain the string not after
this operation.
StringBuffer Objects
String objects cannot be changed, but we have been creating strings that are combinations and
modifications of existing String objects, so how is this done? Java has another standard class for
defining strings, StringBuffer , and a StringBuffer object can be altered directly. Strings that can
be changed are often referred to as mutable strings whereas a String object is an immutable string .
Java uses objects of the class StringBuffer internally to perform many of the operations on String
objects. You can use a StringBuffer object whenever you need a string that you can change directly.