Buggy Example Program

import java.io.*;
class ReadLongs
{
 public static void main ( String[] args ) 
 {
   String fileName = "intData.dat" ;   long sum = 0;

   try
   {      
     DataInputStream instr = 
       new DataInputStream(
         new BufferedInputStream(
           new FileInputStream( fileName  ) ) );

     sum += instr.readLong();
     sum += instr.readLong();
     System.out.println( "The sum is: " + sum );
     instr.close();
   }
   catch ( IOException iox )
   {
     System.out.println("Problem reading " + fileName );
   }
 }
}

The new program reads two 8-byte longs. The previous program read four 4-byte ints. Each program reads the same 16 bytes, but the bytes are grouped in different ways. This new program uses the same data file (and the same bytes) as the previous program.

Here is a sample run:

C:\Programs>java  ReadLongs
The sum is: 1099511627776

C:\Programs>

The program used the same input file and read in the same bytes as the previous program, but computed a different answer. What happened?

Well, this program read the first 8 bytes of the file as a long value. But when those 8 bytes were written, they were intended to be two 4-byte ints. Then the second 8 bytes were read as another long value. But they, also, were intended to be two ints. In other words, the new program interpreted the bytes of the file incorrectly. No wonder it computed a strange answer!

Answer:

Buggy Example Program

QUESTION 4: