Java Reference
In-Depth Information
To test a program, you should provide the input that covers all cases. For this program,
your input should cover all statuses (
0
,
1
,
2
,
3
). For each status, test the tax for each of the six
brackets. So, there are a total of 24 cases.
test all cases
Tip
For all programs, you should write a small amount of code and test it before moving on
to add more code. This is called
incremental development and testing
. This approach
makes testing easier, because the errors are likely in the new code you just added.
incremental development and
testing
3.17
✓
✓
Are the following two statements equivalent?
Check
Point
if
(income <=
10000
)
tax = income *
0.1
;
else if
(income <=
20000
)
tax =
1000
+
(income -
10000
) *
0.15
;
if
(income <=
10000
)
tax = income *
0.1
;
else if
(income >
10000
&&
income <=
20000
)
tax =
1000
+
(income -
10000
) *
0.15
;
The logical operators
!
,
&&
,
||
, and
^
can be used to create a compound Boolean
expression.
Key
Point
Sometimes, whether a statement is executed is determined by a combination of several condi-
tions. You can use logical operators to combine these conditions to form a compound Boolean
expression.
Logical operators
, also known as
Boolean operators
, operate on Boolean values
to create a new Boolean value. Table 3.3 lists the Boolean operators. Table 3.4 defines the
not (
!
) operator, which negates
true
to
false
and
false
to
true
. Table 3.5 defines the and
(
&&
) operator. The and (
&&
) of two Boolean operands is
true
if and only if both operands are
true
. Table 3.6 defines the or (
||
) operator. The or (
||
) of two Boolean operands is
true
if at least one of the operands is
true
. Table 3.7 defines the exclusive or (
^
) operator. The
exclusive or (
^
) of two Boolean operands is
true
if and only if the two operands have differ-
ent Boolean values. Note that
p1 ^ p2
is the same as
p1 != p2
.
T
ABLE
3.3
Boolean Operators
Operator
Name
Description
!
not
logical negation
&&
and
logical conjunction
||
or
logical disjunction
exclusive or
logical exclusion
^
T
ABLE
3.4
Truth Table for Operator
!
p
!p
Example (assume
age = 24, weight = 140
)
true
false
!(age > 18)
is
false
, because
(age > 18)
is
true
.
false
true
!(weight == 150)
is
true
, because
(weight == 150)
is
false
.
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