Posted by : Rhyf Ahmad Thursday, May 21, 2015

If you are new to programming file operations, there are a couple of things about how they work that may not be apparent to you and can be a source of confusion, so I’ll clarify these before I go any further. If you already know how input and output for disk files work, you can skip this section.
First, let’s consider the nature of a file. After you have written data to a file, what you have is just a linear sequence of bytes. The bytes in a file are referenced by their offset from the beginning, so the first byte is byte 0, the next byte is byte 1, the third byte is byte 2, and so on through to the end of the file. If there are n bytes in a file, the last byte is at offset n  1. There is no specific information in the fi le about how the data originated or what it represents unless you explicitly put it there. Even if there is, you need to know that there is information that tells you how the data is formatted, and read and interpret the data accordingly.
For example, if you write a series of 25 binary values of type int to a file, it contains 100 bytes. Nothing in the file indicates that the data consists of 4-byte integers so there is nothing to prevent you from reading the data back as 50 Unicode characters or 10 long values followed by a string, or any other arbitrary collection of data items that corresponds to 100 bytes. Of course, the result is unlikely to be very meaningful unless you interpret the data in the form in which it was originally written. This implies that to read data from a file correctly, you need to have prior knowledge of the structure and format of the data that is in the file.
The form of the data in the file may be recorded or implied in many ways. For example, one way that the format of the data in a file can be communicated is to use a standardized file name extension for data of a particular kind, such as .java for a Java source file or .jpg for a graphical image file or .wav for a sound file. Each type of file has a predefined structure, so from the file extension you know how to interpret the data in the file. Of course, another way of transferring data so that it can be interpreted correctly is to use a generalized mechanism for communicating data and its structure, such as XML. XML files also express form through the file extension .xml. You’ll learn more about XML and how to write and read XML files in the last two chapters of the book.

Contents:

File I/O Basics
File Output
Writing a File via an Output Stream
Writing a File Using a Writer
Buffers
  1. Buffer Capacity
  2. Buffer Position and Limit
  3. Setting the Position and Limit
  4. Creating Buffers
  5. Marking a Buff er
  6. Buffer Data Transfers
  7. Using View Buffers
  8. Preparing a Buff er for Output to a File

Writing a File Using a Channel
  1. Channel Interfaces
  2. Channel Operations
  3. Obtaining a Channel for a File
  4. Channel Write Operations

File Write Operations
  1. Writing Part of a Buffer to a File
  2. File Position
  3. Using a View Buffer to Load a Byte Buffer
  4. Writing Varying Length Strings to a File
  5. Direct and Indirect Buff ers
  6. Writing Numerical Data Using a Channel
  7. Writing Mixed Data to a File
  8. Writing from Multiple Buffers

Forcing Data to Be Written to a Device 



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