How (in general) can IO be made more efficient in this program?

A good answer might be:

By using buffered input and buffered output.

The stream types BufferedInputStream and BufferedOutputStream each put a buffer between the program and the disk. The program logic deals with single bytes; actual IO is done efficiently.

    DataInputStream  instr;
    DataOutputStream outstr;
    . . . .
      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 names of the files come from the command line. The name of the file to be copied is argument number 0; the copy is argument number 2 (the word "to" is argument number 1).

QUESTION 17:

But now there is something else that needs to be handled. What is it?