MATHEMATICAL FUNCTIONS, CHARACTERS, AND STRINGS - Introduction to Java Programming: Comprehensive Version - page 146

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, ..., item k )

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 4.11 lists some frequently used simple format
specifiers.

format specifier

T ABLE 4.11

Frequent ly Used Format Specifiers

Format Specifier Output Example

%b a Boolean value true or false

%c a character 'a'

a decimal integer 200

%d

%f a floating-point number 45.460000

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

%s a string “Java is cool”

Here is an example:

items

int count = 5 ;
double amount = 45.56 ;
System.out.printf( "count is %d and amount is %f", count, amount );

display count is 5 and amount is 45.560000