// newio/LargeMappedFiles.java
// (c)2021 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Creating a very large file using mapping
import java.nio.*;
import java.nio.channels.*;
import java.io.*;

public class LargeMappedFiles {
  static int length = 0x8000000; // 128 MB
  public static void
  main(String[] args) throws Exception {
    try(
      RandomAccessFile tdat =
        new RandomAccessFile("test.dat", "rw")
    ) {
      MappedByteBuffer out = tdat.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));
    }
  }
}
/* Output:
Finished writing
xxxxxx
*/