SELECTIONS - Introduction to Java Programming - page 113

double interest = amount * interestRate;
System.out.println( "Interest is " + interest);

Interest is 16.404674

Because the interest amount is currency, it is desirable to display only two digits after the
decimal point. To do this, you can write the code as follows:

double amount = 12618.98 ;
double interestRate = 0.0013 ;
double interest = amount * interestRate;
System.out.println( "Interest is "
+ ( int )(interest * 100 ) / 100.0 );

Interest is 16.4

However, the format is still not correct. There should be two digits after the decimal point:
16.40 rather than 16.4 . You can fix it by using the printf method, like this:

printf

double amount = 12618.98 ;
double interestRate = 0.0013 ;
double interest = amount * interestRate;
System.out.printf( "Interest is %4.2f" , interest);

format specifier

% 4 .

2 f

field width conversion code

precision

Interest is 16.40

The syntax to invoke this method is

System.out.printf(format, item1, item2, ..., itemk)

where format is a string that may consist of substrings and format specifiers.
A format specifier specifies how an item should be displayed. An item may be a
numeric value, a character, a Boolean value, or a string. A simple format specifier consists
of a percent sign ( % ) followed by a conversion code. Table 3.8 lists some frequently used
simple format specifiers.

format specifier

T ABLE 3.8 Frequently Used Format Specifiers
Format Specifier

Output Example

%b a Boolean value true or false

%c a character 'a'

%d a decimal integer 200

%f a floating-point number 45.460000

%e a number in standard scientific notation 4.556000e ˛ + 01

%s a string “Java is cool”