The JavaTM Tutorial

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Trail: Essential Java Classes
Lesson: Using String and StringBuffer

## Modifying StringBuffers

> The `reverseIt` method uses `StringBuffer`'s `append` method to add a character to the end of the destination string: `dest`.

> >     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();
> >         }
> >     }

> If the appended character causes the size of the `StringBuffer` to grow beyond its current capacity, the `StringBuffer` allocates more memory. Because memory allocation is a relatively expensive operation, you can make your code more efficient by initializing a `StringBuffer`'s capacity to a reasonable first guess, thereby minimizing the number of times memory must be allocated for it. For example, the `reverseIt` method constructs the `StringBuffer` with an initial capacity equal to the length of the source string, ensuring only one memory allocation for `dest`.

> The version of the `append` method used in `reverseIt` is only one of the `StringBuffer` methods that appends data to the end of a `StringBuffer`. There are several `append` methods that append data of various types, such as `float`, `int`, `boolean`, and even `Object`, to the end of the `StringBuffer`. The data is converted to a string before the append operation takes place.

### Inserting Characters

> At times, you may want to insert data into the middle of a `StringBuffer`. You do this with one of StringBufffer's `insert` methods. This example illustrates how you would insert a string into a `StringBuffer`:

> >     StringBuffer sb = new StringBuffer("Drink Java!");
> >     sb.insert(6, "Hot ");
> >     System.out.println(sb.toString());

> This code snippet prints:

> >     Drink Hot Java!

> With `StringBuffer`'s many `insert` methods, you specify the index before which you want the data inserted. In the example, "Hot " needed to be inserted before the 'J' in "Java". Indices begin at 0, so the index for 'J' is 6. To insert data at the beginning of a `StringBuffer`, use an index of 0. To add data at the end of a `StringBuffer`, use an index equal to the current length of the `StringBuffer` or use `append`.

### Setting Characters

> Another useful `StringBuffer` modifier is `setCharAt`, which replaces the character at a specific location in the `StringBuffer` with the character specified in the argument list.. `setCharAt` is useful when you want to reuse a `StringBuffer`.

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