Data Types and Conditional Statements - Learning Java Through Games - page 28

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.