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Why Two String Classes?

The Java platform provides two classes, String and StringBuffer, that store and manipulate strings-character data consisting of more than one character. The String class provides for strings whose value will not change. For example, if you write a method that requires string data and the method is not going to modify the string in any way, pass a String object into the method. The StringBuffer class provides for strings that will be modified; you use string buffers when you know that the value of the character data will change. You typically use string buffers for constructing character data dynamically: for example, when reading text data from a file. Because strings are constants, they are more efficient to use than are string buffers and can be shared. So it's important to use strings when you can.

Following is a sample program called StringsDemo, which reverses the characters of a string. This program uses both a string and a string buffer.

public class StringsDemo {
    public static void main(String[] args) {
        String palindrome = "Dot saw I was Tod";
        int len = palindrome.length();
        StringBuffer dest = new StringBuffer(len);

        for (int i = (len - 1); i >= 0; i--) {
            dest.append(palindrome.charAt(i));
        }
        System.out.println(dest.toString());
    }
}

The output from this program is:

doT saw I was toD

In addition to highlighting the differences between strings and string buffers, this section discusses several features of the String and StringBuffer classes: creating strings and string buffers, using accessor methods to get information about a string or string buffer, and modifying a string buffer.

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