The String and StringBuffer Classes

Creating Strings and StringBuffers

The bold line in the reverseIt method creates a StringBuffer named dest whose initial length is the same as source.

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 code StringBuffer dest declares to the compiler that dest will be used to refer to an object whose type is StringBuffer, the new operator allocates memory for a new object, and StringBuffer(len) initializes the object. These three steps--declaration, instantiation, and initialization--are described in Creating Objects.

Creating a String

Many Strings are created from string literals. When the compiler encounters a series of characers enclosed in double quotes, it creates a String object whose value is the text that appeared between the quotes. When the compiler encounters the following string literal, it creates a String object whose value is Gobbledy gook.

"Gobbledy gook."

You can also create String objects as you would any other Java object: using the new keyword.

new String("Gobbledy gook.");

Creating a StringBuffer

The constructor method used by reverseIt to initialize the dest requires an integer argument indicating the initial size of the new StringBuffer.

StringBuffer(int length)

reverseIt could have used StringBuffer's default constructor that leaves the buffer's length undetermined until a later time. However, it's more efficient to specify the length of the buffer if you know it, instead of allocating more memory every time you append a character to the buffer.

The String and StringBuffer Classes