Writing Data to a Sequential Data File - Java Programming: Comprehensive Concepts and Techniques - page 506

Data File Concepts
Programs often need to read data from a data file or write data to a data file on a
secondary storage device, such as a disk. Storing data in locations within the
computer's memory is temporary; data easily can be overwritten or lost when
the computer is turned off. Therefore, any permanent storage of data should be
on a secondary storage device. Data typically is stored in data files, which are
collections of fields within records.
To read data, a Java program must open a stream to the data file. Once the
data source is streamed, Java reads the information serially. Similarly, a Java pro-
gram can write data to a secondary storage device by opening a stream to the
data and writing the data serially.

Data Hierarchy

Data is organized in a hierarchy, in which each level contains one or more
elements from the level beneath it. The levels in the hierarchy of data, from low-
est to highest, are bit, byte, field, record, and file (Table 8-6).

Table 8-6 Hierarchy of Data

DATA ELEMENT CONTAINS DESCRIPTION EXAMPLE

bit lowest level binary digit 0 or 1 Bits can represent any two-state

condition, such as on or off, but
usually are combined with bytes
to represent data

byte group of related bits one character or other unit of 01000001 (letter A)

information consisting of
eight bits

field group of related bytes individual elements of data, Ethel

such as a person's first name

record group of related fields related groups of fields, such Ethel Malson

as a person's name, address, 202 N. Van Buren

and telephone number Albany, MO 64402

[phone]

file group of related records Many related records Ethel Malson, 202 N. Van

Buren…
Idris Evans, R.R. 1 Box 199…
Elsie Amos, 1306 Minuteman
Dr.…

All data in memory appears as combinations of zeroes and ones, because
electronic devices can assume one of two stable states: off and on. This binary
digit , or bit , is the smallest piece of data a computer can understand. Usually a
bit is combined with other bits to represent data. The combination of bits
within a coding scheme is called a byte . A byte can represent a character, such as