if Statement
In its most basic form, an if
statement executes a single statement or a block of statements if a boolean
expression evaluates to true
. Here’s the syntax:
if (boolean-expression)
statement
The boolean
expression must be enclosed in parentheses. If you use only a single statement, it must end with a semicolon. However, the statement can also be a statement block enclosed by braces. In that case, each statement within the block needs a semicolon, but the block itself doesn’t.
Here’s an example:
double commissionRate = 0.0;
if (salesTotal > 10000.0)
commissionRate = 0.05;
In this example, a variable named commissionRate
is initialized to 0.0
and then set to 0.05
if salesTotal
is greater than 10000.0
.
Here’s an example that uses a block rather than a single statement:
double commissionRate = 0.0;
if (salesTotal > 10000.0)
{
commissionRate = 0.05;
commission = salesTotal * commissionRate;
}
In this example, the two statements within the braces are executed if salesTotal
is greater than $10,000. Otherwise, neither statement is executed.
An if
statement can include an else
clause that executes a statement or block if the boolean
expression is not true
. Its basic format is
if (boolean-expression)
statement
else
statement
Here’s an example:
double commissionRate;
if (salesTotal <= 10000.0)
commissionRate = 0.02;
else
commissionRate = 0.05;
In this example, the commission rate is set to 2% if the sales total is less than or equal to $10,000. If the sales total is greater than $10,000, the commission rate is set to 5%.
Here’s an if
statement with an else
clause that uses a block instead of a single statement:
double commissionRate;
if (salesTotal <= 10000.0)
{
commissionRate = 0.02;
level1Count++;
}
else
{
commissionRate = 0.05;
level2Count++;
}
The statement that goes in the if
or else
part of an if-else
statement can be any kind of Java statement, including another if
or if-else
statement. This arrangement is nesting, and an if
or if-else
statement that includes another if
or if-else
statement is a nested if
statement.
The general form of a nested if
statement is this:
if (expression-1)
if (expression-2)
statement-1
else
statement-2
else
if (expression-3)
statement-3
else
statement-4
In this example, expression-1
is the first to be evaluated. If it evaluates to true
, expression-2
is evaluated. If that expression is true
, statement-1
is executed; otherwise, statement-2
is executed. But if expression-1
is false
, expression-3
is evaluated. If expression-3
is true
, statement-3
is executed; otherwise, statement-4
is executed.
Here’s an example that implements a complicated commission structure based on two variables, named salesClass
and salesTotal
:
if (salesClass == 1)
if (salesTotal < 10000.0)
commissionRate = 0.02;
else
commissionRate = 0.04;
else
if (salesTotal < 10000.0)
commissionRate = 0.025;
else
commissionRate = 0.05;