Java Reference

In-Depth Information

TABLE 2 . 3 :
Java operators on Boolean values.

Operator Meaning Example

&&

and

T&&T=T T&&F=F F&&F=F

||

or

T

||

F=T T

||

T=T F

||

F=F

!

negation !T=F, !F=T

, is enclosed in single quotes. Conversely, a

string value, such as
"cat"
, is enclosed in double quotes. The above implementation is not

optimal. The second
if
statement can be misleading. A user may interpret it that
grade=

Note that a character literal, such as

'

A

'

'

when
x<
= 100. However,
x
must be also greater or equal to 90. Nested
if
statements can

quickly get confusing to interpret. Therefore, a good programming practice is to never have

too many nested
if
statements and avoid them if at all possible. A better implementation

is to combine the two
if
statements into a single
if
statement. Here is how this can be

done.

if
(x

'

A

>

=90&&x

<

= 100)

{

grade =
'A'
;

}

The “&&” operator is an operator that works on
boolean
values (i.e.,
true
/
false

values). It is the logical “and”. For example, the “+” operator can be used to add two

integers and return an integer. Conversely, the “&&” operator takes as input two
boolean

values and produces a
boolean
value. Java supports three operators on Boolean values; see

Table 2.3.

For example, if we want to give a letter grade of

(i.e., other) when the numeric

grade is smaller than 0 or bigger than 100, we can write the following code.

'O'

if
(x
>
100

||

x
<
0)
{

grade =
'O'
;

}

The operator “——” is the logical or operator. Note that the condition
(x>100 && x<0)

is not meaningful because
x
cannot be bigger than 100 and smaller than 0 at the same time.

The next statement is a rewrite of the last code snippet that uses the negation operator.

if
!(x
<
= 100 && x
>
=0)
{

grade =

'O'

;

}

We will go inside the
if
statement when it is not true that
x
is between 0 and 100. Note

that the following code snippet will not compile.

if
!(0
<
=x
<
= 100)
{

grade =
'O'
;

}

Thereasonisthat0
<
=
x
<
= 100 is not a valid condition. This is a statement that can

be written in math, but it is not recognized by the Java compiler. One rule to remember

is that the condition of an
if
statement must always be surrounded by parentheses. For

example, the following code snippet will produce a syntax error.

if
x
<
60
{

grade =
'F'
;

}

Our complete program is shown next.