Java Reference
In-Depth Information
Static Variables
A
static variable
belongs to the class as a whole. All objects of the class can read and
change the static variable. Static variables should normally be private, unless they happen to
be defined constants.
SYNTAX
private static
Type Variable_Name;
private static
Type Variable_Name = Initial_Value;
public static final
Type Variable_Name = Constant_Value;
EXAMPLES
private static
String lastUser;
private static int
turn = 0;
public static final double
PI = 3.14159;
Self-Test Exercises
7. What is the difference between a static variable and an instance variable?
8. Can you use an
instance variable
(without an object name and dot) in the
defi nition of a
static method
of the same class? Can you use an
instance variable
(without an object name and dot) in the defi nition of a
nonstatic (ordinary)
method
of the same class?
9. Can you use a
static variable
in the defi nition of a static method of the same
class? Can you use a
static variable
in the defi nition of a
nonstatic (ordinary)
method
of the same class?
10. Can you use the
this
parameter in the defi nition of a static method?
11. When we defi ned the class
Date
in Display 4.11 in Chapter 4 , we had not
yet discussed static methods, so we did not mark any of the methods
static
.
However, some of the methods could have been marked
static
(and should
have been marked
static
, if only we had known what that meant). Which of
the methods can be marked
static
? (If you omit the modifi er
static
when it
is appropriate, then the method cannot be invoked with the class name; it must
be invoked with a calling object.)
12. Following the style guidelines given in this topic, when should a static variable
be marked
private
?
13. What do static methods and static variables have in common? After all, they are
both called
static
, so it sounds like they have something in common.
