Java Reference
In-Depth Information
Although there are only two logical values,
true
and
false
, they are extremely useful
because they permit programs to incorporate decision making that alters the processing
flow. The remainder of this chapter discusses ways to incorporate decisions into a
program. Java has three selection or branch control structures:
if
and
if
...
else
statements, and the
switch
structure. This section discusses how
if
and
if
...
else
statements can be used to create one-way selection, two-way selection, and multiple
selections. The
switch
structure is discussed later in this chapter.
A bank wants to send a notice to a customer if her or his checking account balance falls below
the required minimum balance. That is, if the balance is below the required minimum, the
bank should send a notice to the customer; otherwise, it should do nothing.Similarly,ifthe
policyholder of an insurance policy is a nonsmoker, the company wants to apply a 10% discount
to the policy premium. Both of these examples involve one-way selection. In Java, one-way
selections are incorporated using the
if
statement. The syntax of one-way selection is:
if
(logical expression)
statement
Note the elements of this syntax. It begins with the reserved word
if
, followed by a
logical expression
contained within parentheses, followed by a
statement
. The
logical expression
is also called a condition; it decides whether to execute the
statement
that follows it. If
logical expression
is
true
, the
statement
executes. If
it is
false
, the
statement
does not execute and the computer goes on to the next
statement in the program. The
statement
following the
logical expression
is
sometimes called the action statement. (Note the indentation of the action
statement
.
We have indented it four spaces to the right of the
if
statement in the previous line.)
Figure 4-2 shows the flow of execution of the
if
statement (one-way selection).
logical expression
true
statement
false
FIGURE 4-2
One-way selection
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