Java Tutorial/File/Memory File

Memory-Mapped Files

   <source lang="java">

import java.io.File; import java.io.RandomAccessFile; import java.nio.MappedByteBuffer; import java.nio.channels.FileChannel; public class MainClass {

 public static void main(String[] args) throws Exception {
   File aFile = new File("C:/test.bin");
   RandomAccessFile ioFile = new RandomAccessFile(aFile, " rw");
   FileChannel ioChannel = ioFile.getChannel();
   final int PRIMESREQUIRED = 10;
   long[] primes = new long[PRIMESREQUIRED];
   int index = 0;
   final long REPLACEMENT = 999999L;
   final int PRIMECOUNT = (int) ioChannel.size() / 8;
   MappedByteBuffer buf = ioChannel.map(FileChannel.MapMode.READ_WRITE, 0L, ioChannel.size())
       .load();
   ioChannel.close();
   for (int i = 0; i < PRIMESREQUIRED; i++) {
     index = 8 * (int) (PRIMECOUNT * Math.random());
     primes[i] = buf.getLong(index);
     buf.putLong(index, REPLACEMENT);
   }
   for (long prime : primes) {
     System.out.printf("%12d", prime);
   }
   ioFile.close();
 }

}</source>