import java.io.*;
import java.nio.*;
import java.nio.channels.*;
public class LargeMappedFiles {
   static int length = 0x8FFFFFF; // 128 Mb
   public static void main(String[] args) throws Exception {
     MappedByteBuffer out = 
       new RandomAccessFile("test.dat", "rw").getChannel()
       .map(FileChannel.MapMode.READ_WRITE, 0, length);
     for(int i = 0; i < length; i++)
       out.put((byte)'x');
     System.out.println("Finished writing");
     for(int i = length/2; i < length/2 + 6; i++)
       System.out.print((char)out.get(i));    //read file
   }
} ///