Here is an example of how to use the SegmentedStringWriter class from the Apache Commons IO library:

import org.apache.commons.io.output.SegmentedStringWriter;

public class Example {
    public static void main(String[] args) {
        // Create a SegmentedStringWriter
        SegmentedStringWriter writer = new SegmentedStringWriter();

        // Write some data to the writer
        writer.write("Hello ");
        writer.write("world!");
        writer.write(" This is an example.");

        // Get the written data as a String
        String data = writer.toString();

        // Print the data
        System.out.println(data);

        // Clear the writer
        writer.reset();

        // Write some more data to the writer
        writer.write("This is a new segment.");

        // Get the new data as a String
        String newData = writer.toString();

        // Print the new data
        System.out.println(newData);

        // Close the writer
        writer.close();
    }
}

In this example, the SegmentedStringWriter class is being used to write data to a String. The write method is used to write data to the SegmentedStringWriter. The toString method is used to get the written data as a String. The reset method is used to clear the written data. The close method is used to close the SegmentedStringWriter and release any resources.

The SegmentedStringWriter class is useful when you want to write data to a String, but you want to be able to clear the data and write new data to the same writer object. This can be useful for example when you want to write data to a string in multiple steps, but you don't want to create a new StringWriter for each step.

It's worth noting that the SegmentedStringWriter class is a subclass of the StringWriter class, so it has all the functionality of the StringWriter class, but with the added ability to clear the written data.