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Strings

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 section 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.

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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.

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This section covers these string-related topics:

• Why Two String Classes?
• Creating Strings and StringBuffers
• Accessor Methods
• Modifying StringBuffers
• Converting Objects to Strings
• Converting Strings to Numbers
• Strings and the Java Compiler

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