Console Input and Output, Exercises of Java Programming

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Adapted from Absolute Java, Rose Williams, Binghamton University

Module 3

Console Input and Output

System.out.println for console output  (^) System.out is an object that is part of the Java language  (^) println is a method invoked by the System.out object that can be used for console output  (^) The data to be output is given as an argument in parentheses  (^) A plus sign is used to connect more than one item  (^) Every invocation of println ends a line of output System.out.println("The answer is " + 42);

Formatting Output with printf  (^) Starting with version 5.0, Java includes a method named printf that can be used to produce output in a specific format  (^) The Java method printf is similar to the print method  (^) Like print, printf does not advance the output to the next line  (^) System.out.printf can have any number of arguments  (^) The first argument is always a format string that contains one or more format specifiers for the remaining arguments  (^) All the arguments except the first are values to be output to the screen

printf Format Specifier  The code double price = 19.8; System.out.print("$"); System.out.printf("%6.2f", price); System.out.println(" each"); will output the line $ 19.80 each  The format string "%6.2f" indicates the following:  End any text to be output and start the format specifier (%)  (^) Display up to 6 right-justified characters, pad fewer than six characters on the left with blank spaces (i.e., field width is 6 )  Display exactly 2 digits after the decimal point (.2)  (^) Display a floating point number, and end the format specifier (i.e., the conversion character is f)

Line Breaks with printf

 Line breaks can be included in a format string

using %n

 The code

double price = 19.8; String name = "magic apple";

System.outprintf("$%6.2f for each

%s.%n", price, name);

System.out.println("Wow");

will output

$ 19.80 for each magic apple. Wow

Format Specifiers for System.out.printf

The printf Method (2/3)

The printf Method (3/3)

Money Formats  (^) Using the NumberFormat class enables a program to output amounts of money using the appropriate format  (^) The NumberFormat class must first be imported in order to use it

import java.text.NumberFormat

 (^) An object of NumberFormat must then be created using the getCurrencyInstance() method  (^) The format method takes a floating-point number as an argument and returns a String value representation of the number in the local currency

Money Formats import java.text.NumberFormat; public class CurrencyFormatDemo { public static void main(String[] args) { System.out.println("Default location:"); NumberFormat moneyFormater = NumberFormat.getCurrencyInstance(); System.out.println(moneyFormater.format(19.8)); System.out.println(moneyFormater.format(19.81111)); System.out.println(moneyFormater.format(19.89999)); System.out.println(moneyFormater.format(19)); System.out.println(); } }

Specifying Locale

 Invoking the getCurrencyInstance()

method without any arguments produces an

object that will format numbers according to

the default location

 In contrast, the location can be explicitly

specified by providing a location from the

Locale class as an argument to the

getCurrencyInstance() method

 When doing so, the Locale class must first

be imported

import java.util.Locale;

Specifying Locale import java.text.NumberFormat; import java.util.Locale; public class CurrencyFormatDemo { public static void main(String[] args) { System.out.println("US as location:"); NumberFormat moneyFormater2 = NumberFormat.getCurrencyInstance(Locale.US); System.out.println(moneyFormater2.format(19.8)); System.out.println(moneyFormater2.format(19.81111)); System.out.println(moneyFormater2.format(19.89999)); System.out.println(moneyFormater2.format(19)); } }

Locale Constants for Currencies of Different Countries

The DecimalFormat Class  (^) Using the DecimalFormat class enables a program to format numbers in a variety of ways  (^) The DecimalFormat class must first be imported  (^) A DecimalFormat object is associated with a pattern when it is created using the new command  (^) The object can then be used with the method format to create strings that satisfy the format  (^) An object of the class DecimalFormat has a number of different methods that can be used to produce numeral strings in various formats