CONTROL STRUCTURES I: SELECTION - Java Programming: From Problem Analysis to Program Design - page 194

EXAMPLE 4-10

Consider the following statements:

if (hours > 40.0) //Line 1

wages = 40.0 * rate +
1.5 * rate * (hours - 40.0); //Line 2

else //Line 3

wages = hours * rate; //Line 4

If the value of the variable hours is greater than 40.0 , then the wages include overtime
payment. Suppose that hours is 50 . The logical expression in the if statement in Line 1
evaluates to true , so the statement in Line 2 executes. On the other hand, if hours is 30 ,
or any number less than or equal to 40 , the logical expression in the if statement in Line
1 evaluates to false . In this case, the program skips the statement in Line 2 and executes
the statement in Line 4—that is, the statement following the reserved word else
executes.

In a two-way selection statement, putting a semicolon after the right parenthesis and
before statement1 creates a syntax error. If the if statement ends with a semicolon,
statement1 is no longer part of the if statement, and the else part of the if ... else
statement stands by itself. There is no stand-alone else statement in Java; that is, the
else statement cannot be separated from the if statement. This also creates a syntax
error.

EXAMPLE 4-11

The following statements show an example of a syntax error:

if (hours > 40.0); //Line 1

wages = 40.0 * rate +
1.5 * rate * (hours - 40.0); //Line 2
else //Line 3
wages = hours * rate; //Line 4
Because a semicolon follows the closing parenthesis of the if statement (Line 1), the
else statement stands alone. The semicolon at the end of the if statement (see Line 1)
ends the if statement, so the statement in Line 2 separates the else clause from the if
statement. That is, else is by itself. Because there is no separate else statement in Java,
this code generates a syntax error.