A good answer might be:

Exceptions may be thrown when the files are opened.

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.

QUESTION 18:

What might go wrong inside the outer try{} block which would cause an exception?