Flow of Control - Java - page 113

Building Boolean Expressions
You can combine two Boolean expressions using the “and” operator, which is spelled
&& in Java. For example, the following Boolean expression is true provided number is
greater than 2 and number is less than 7:

&& means
“and”

(number > 2) && (number < 7)

When two Boolean expressions are connected using &&, the entire expression is true ,
provided both of the smaller Boolean expressions are true ; otherwise, the entire
expression is false .

The “and” Operator &&
You can form a more elaborate Boolean expression by combining two simpler Boolean
expressions using the “and” operator && .
SYNTAX (FOR A BOOLEAN EXPRESSION USING && )

( Boolean_Exp_1 ) && ( Boolean_Exp_2 )
EXAMPLE (WITHIN AN if-else STATEMENT)

if ( (score > 0) && (score < 10) )
System.out.println("score is between 0 and 10.");
else
System.out.println("score is not between 0 and 10.");

If the value of score is greater than 0 and the value of score is also less than 10, then the first
System.out.println statement is executed; otherwise, the second System.out.println
statement is executed.

|| means “or”

You can also combine two Boolean expressions using the “or” operator, which is
spelled || in Java. For example, the following is true provided count is less than 3 or
count is greater than 12:

(count < 3) || (count > 12)

When two Boolean expressions are connected using || , the entire expression is true ,
provided that one or both of the smaller Boolean expressions are true ; otherwise, the
entire expression is false .
You can negate any Boolean expression using the ! operator. If you want to negate
a Boolean expression, place the expression in parentheses and place the ! operator in
front of it. For example, !(savings < debt) means “savings is not less than debt.”
The ! operator can usually be avoided. For example,

!(savings < debt)

is equivalent to savings >= debt . In some cases, you can safely omit the parentheses,
but the parentheses never do any harm. The exact details on omitting parentheses are
given in the subsection entitled “Precedence and Associativity Rules.”