Java Reference
In-Depth Information
Why Eight Bits?
A
byte
is a memory location that can hold eight bits. What is so special about eight
?
Why not
ten bits
?
There are two reasons why eight is special. First, eight is a power of 2 (8 is 2
3
).
Since computers use bits, which have only two possible values, powers of 2 are more conve-
nient than powers of 10. Second, it turns out that seven bits are required to code a single
character of the ASCII character set. So eight bits (one byte) is the smallest power of 2 that
will hold a single ASCII character.
Display 5.10
Variables in Memory
Main Memory
byte 0
byte 1
byte 2
byte 3
byte 4
byte 5
byte 6
byte 7
byte 8
variable1
(3-byte location with address 0)
variable2
(2-byte location with address 3)
variable3
(1-byte location with address 5)
variable4
( 3-byte location with address 6 )
References
In order to have a simple example to help explain
references
, we will use the class
ToyClass
defined in Display 5.11.
Variables of a class type name objects of their class differently than how variables of
primitive types, such as
int
or
char
, store their values. Every variable, whether of a
primitive type or a class type, is implemented as a location in the computer memory.
For a variable of a primitive type, the value of the variable is stored in the memory
location assigned to the variable. However, a variable of a class type stores only the
memory address of where an object is located. The object named by the variable is
stored in some other location in memory, and the variable contains only the memory
