Opening the Files

The constructors for FileInputStream and for FileOutputStream throw exceptions which need to be caught. This calls for an outer try{} block:

DataInputStream  instr;
DataOutputStream outstr;
. . . . 
try
{
  instr = 
    new DataInputStream(
      new BufferedInputStream(
        new FileInputStream( args[0] )));
  
  outstr = 
    new DataOutputStream(
      new BufferedOutputStream(
        new FileOutputStream( args[2] )));
  
  try
  {
    int data;
    while ( true )
    {
      data = instr.readUnsignedByte() ;
      outstr.writeByte( data ) ;
    }
  }
  
  catch ( EOFException  eof )
  {
    outstr.close();
    instr.close();
    return;
  }
  
}

The outer try{} block encloses the constructors and the IO loop.