5. Example: FileChannel and ByteBuffer classes

• 
  import java.nio.file.*;
  import java.io.*;
  import java.nio.channels.FileChannel;
  import java.nio.ByteBuffer;
  import static java.nio.file.StandardOpenOption.*;
  public class RandomAccessTest
  {
      public static void main(String[] args)
      {
          Path file =
              Paths.get("C:/example/mydata.txt");
          String s = "XYZ";
          byte[] data = s.getBytes();
          ByteBuffer out = ByteBuffer.wrap(data);
          FileChannel fc = null;
          try
          {
              fc = (FileChannel)Files.newByteChannel(file, CREATE, WRITE);
              // starting at the beginning of the file
              fc.position(0);
              // as long as there are bytes in the buffer,
              while(out.hasRemaining()) {
                  // write sequence of bytes from the buffer
                  fc.write(out);
              }
              // reset the buffer position back to the beginning
              out.rewind();
  
              // reposition the file location at offset 22
              // NOTE: the unfilled gaps are stored as zero bytes
              fc.position(22);
              // as long as there are bytes in the buffer,
              while(out.hasRemaining()) {
                  // write sequence of bytes from the buffer
                  fc.write(out);
              }
              // reset the buffer position back to the beginning
              out.rewind();
              // reposition the file location at offset 12
              fc.position(12);
              while(out.hasRemaining()) {
                  // write sequence of bytes from the buffer
                  fc.write(out);
              }
              fc.close();
          }
          catch (Exception e)
          {
              System.out.println("Error message: " + e);
          }
      }
  } // class RandomAccessTest