Leer bytes de FileInputStream en Java

import java.io.File;
import java.io.FileInputStream;
public class fileInputStream {
    public static void main(String[] args) {
        byte[] data = new byte[1024]; //allocates memory for 1024 bytes
        //be careful about how to declare an array in Java
        int readBytes;
        try {
            File file = new File("testfile");
            file.createNewFile();
            FileInputStream in = new FileInputStream(file);
 
            while ((readBytes = in.read(data)) != -1) {
             //read(byte[] b)
             //Reads some number of bytes from the input stream and stores them into the buffer array b.
                System.out.println("read " + readBytes + " bytes, and placed them into temp array named data");
                System.out.println("data :" + data[123]);
            }
            in.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}