Online Test Banks
Score higher
See Online Test Banks
eLearning
Learning anything is easy
Browse Online Courses
Mobile Apps
Learning on the go
Explore Mobile Apps
Dummies Store
Shop for books and more
Start Shopping

How to Use if Statements in Java

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;

The trick of using nested if statements is knowing how Java pairs else keywords with if statements. The rule is actually very simple: Each else keyword is matched with the most previous if statement that hasn’t already been paired with an else keyword.

  • Add a Comment
  • Print
  • Share
blog comments powered by Disqus
Advertisement

Inside Dummies.com

Dummies.com Sweepstakes

Win $500. Easy.