Java Reference
In-Depth Information
Consider the following expression:
8 < '5'
You might think that
8
is being compared with
5
. This is not the case. Here, the
integer
8
is being compared with the character
5
. That is,
8
is being compared with
the Unicode collating sequence of
'5'
, which is
53
. The Java system uses implicit
type conversion, changes
'5'
to
53
, and compares
8
with
53
. Therefore, the expression
8 < '5'
always evaluates to
true
. However, the expression
8 < 5
always evaluates to
false
. Note that
char
and
int
are of integral type and using explicit or implicit type
conversion, values of
char
type can be converted to
int
type and vice versa.
4
Expressions such as
4 < 6
and
'R' > 'T'
are examples of logical (boolean) expressions.
When Java evaluates a logical expression, it returns the
boolean
value
true
if the logical
expression evaluates to
true
; it returns the
boolean
value
false
otherwise.
Expressions
This section describes how to form and evaluate logical expressions that are combina-
tions of other logical expressions. Logical (Boolean) operators enable you to
combine logical expressions. Java has three logical (boolean) operators, as shown in
Table 4-4.
TABLE 4-4
Logical (Boolean) Operators in Java
Operator
Description
!
not
&&
and
||
or
Logical operators take only logical values as operands and yield only logical values as
results. The operator
!
is unary, so it has only one operand. The operators
&&
and
||
are
binary.
Table 4-5 shows that when you use the
!
operator,
!
true
is
false
and
!
false
is
true
. Putting
!
in front of a logical expression reverses the value of that logical expression.
Table 4-5 is called the truth table of the operator
!
. Example 4-1 gives examples of
the
!
operator.
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