Trail:
Essential Java Classes
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The String and StringBuffer Classes
The java.lang package contains two string classes:
String
and
StringBuffer.
You've already seen the String class on several occasions in this tutorial.
You use the String class when you are working with strings that cannot change.
StringBuffer, on the other hand, is used when you want to manipulate the contents
of the string on the fly.
The reverseIt method in the following code uses both
the String and StringBuffer classes to reverse the characters
of a string. If you have a list of words, you can use this method in
conjunction with a sort program to create a list of rhyming words (a
list of words sorted by ending syllables). Just
reverse all the strings in the list, sort the list, and reverse
the strings again. You can see the reverseIt method
producing rhyming words in the example in
How to Use Pipe Streams that shows you how to use piped streams.
public class ReverseString {
public static String reverseIt(String source) {
int i, len = source.length();
StringBuffer dest = new StringBuffer(len);
for (i = (len - 1); i >= 0; i--)
dest.append(source.charAt(i));
return dest.toString();
}
}
The reverseIt method accepts an argument of type String
called source that contains the string data to be reversed.
The method creates a StringBuffer, dest, the same size as
source. It then loops backwards over all the
characters in source and appends them to dest,
thereby reversing the string.
Finally, the method converts dest, a StringBuffer, to a String.
In addition to highlighting the differences between Strings and StringBuffers,
this lesson illustrates several features of the String and StringBuffer classes:
creating Strings and StringBuffers, using accessor methods to get information
about a String or StringBuffer, modifying a StringBuffer, and converting one
type of string to another.
Note to C and C++ Programmers:
Java strings are first-class objects,
unlike C and C++ strings,
which are simply null-terminated arrays
of 8-bit characters.
The Java development environment provides two classes
that store and manipulate character data:
String, for constant strings, and StringBuffer,
for strings that can change.
The following statement taken from the reverseIt method
creates a new StringBuffer
in three steps: declaration, instantiation,
and initialization.
StringBuffer dest = new StringBuffer(len);
These are the same steps for creating an object of any type.
The reverseIt method uses two accessor methods to
obtain information about the source string: charAt and
length.
Both String and StringBuffer provide a number of other accessor methods,
including some
for inspecting substrings and getting the positions of a specific character.
The reverseIt method uses StringBuffer's append
method to add characters to dest. In addition to append,
StringBuffer provides methods to insert characters into the buffer,
modify a character at a specific location within the buffer, and so on.
reverseIt converts the resulting StringBuffer
to a String and returns the string. You can convert several different data types
to Strings using String's valueOf method.
You can also use methods from the Integer,
Float, Double, and Long classes
to convert the contents of a String to a number.
The Java compiler
uses Strings and StringBuffers
behind the scenes to handle literal strings
and concatenation.
Other Interesting Features
String and StringBuffer provide several other useful ways to manipulate
string data, including concatenation, comparison, substitution, and conversion to
upper and lower case.
java.lang.String and
java.lang.StringBuffer summarize and list all of the methods and variables supported by these two classes.
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