1. 28
Formatted Output

2. OBJECTIVES In this chapter you will learn:
To understand input and output streams.
To use printf formatting.
To print with field widths and precisions.
To use formatting flags in the printf format string.
To print with an argument index.
To output literals and escape sequences.
To format output with class Formatter.

3. 28.1   Introduction
28.2   Streams
28.3   Formatting Output with printf
28.4   Printing Integers
28.5   Printing Floating-Point Numbers
28.6   Printing Strings and Characters
28.7   Printing Dates and Times
28.8   Other Conversion Characters
28.9   Printing with Field Widths and Precisions
28.10   Using Flags in the printf Format String
28.11   Printing with Argument Indices
28.12   Printing Literals and Escape Sequences
28.13   Formatting Output with Class Formatter
28.14   Wrap-Up

4. 28.1 Introduction Method printf Class Formatter
Formats and outputs data to the standard output stream, System.out
Class Formatter
Formats and outputs data to a specified destination
E.g., a string or a file output stream

5. 28.2 Streams Streams Sequences of bytes Can often be redirected
Standard input – keyboard
Standard output – screen
Standard error – screen
More in Chapters 14 and 24

6. 28.3 Formatting Output with printf
Precise output formatting
Conversion specifications: flags, field widths, precisions, etc.
Can perform
rounding
aligning columns
right/left justification
inserting literal characters
exponential format
octal and hexadecimal format
fixed width and precision
date and time format

7. 28.3 Formatting Output with printf (Cont.)
Format String
Describe the output format
Consist of fixed text and format specifier
Format specifier
Placeholder for a value
Specify the type of data to output
Begins with a percent sign (%) and is followed by a conversion character
E.g., %s, %d
Optional formatting information
Argument index, flags, field width, precision
Specified between % and conversion character

8. 28.4 Printing Integers Integer Format
Whole number (no decimal point): 25, 0, -9
Positive, negative, or zero
Only minus sign prints by default (later we shall change this)
Format
printf( format-string, argument-list );
format-string
Describe the output format
argument-list
Contain the value corresponding to each format specifier

9. Fig. 28.1 | Integer conversion characters.

10. Outline Output positive and negative integers
IntegerConversionT est.java
Lines 8-10
Line 11
Line 12
Line 13
Program output
Output positive and negative integers
Output the integer in octal format
Output the integer in hexadecimal format
Output the integer in hexadecimal format with capital letters

11. 28.5 Printing Floating-Point Numbers
Have a decimal point (33.5)
Computerized scientific notation (exponential notation)
is x 10² in scientific
is e+02 in exponential (e stands for exponent)
use e or E
f – print floating point with at least one digit to left of decimal
g (or G) - prints in f or e (E)
Use exponential if the magnitude is less than 10-3, or greater than or equal to 107

12. Fig. 28.3 | Floating-point conversion characters.

13. Outline
FloatingNumberTest .java
Lines 8-10
Line 11
Line 12
Lines 13-14
Program output
Output positive and negative floating-point numbers using the e conversion character
Output floating-point number with uppercase E preceding the exponent
Output floating-point number using the f conversion character
Output floating-point number using the g and G conversion character

14. 28.6 Printing Strings and Characters
Conversion character c and C
Require char
C displays the output in uppercase letters
Conversion character s and S
String
Object
Implicitly use object’s toString method
S displays the output in uppercase letters

15. Common Programming Error 28.1
Using %c to print a string causes an IllegalFormatConversionException—a string cannot be converted to a character.

16. Outline Display character with conversion character c
CharStringConversi on.java
Line 12
Line 13
Lines 14-15
Line 16
Program output
Display character with conversion character c
Display string with conversion character s
Display string with conversion characters s and S
Display Integer object with conversion characters s

17. 28.7 Printing Dates and Times
Conversion characters t and T
Print dates and times in various formats
Followed by a conversion suffix character
Require the corresponding argument to be of type long, Long, Calendar or Date
Conversion suffix characters
Specify the date and/or time format
Format date and time compositions
Format date
Format time

18. Fig. 28.6 | Date and time composition conversion suffix characters.

19. Fig. 28.7 | Date formatting conversion suffix characters.

20. Fig. 28.8 | Time formatting conversion suffix characters.

21. Outline
DateTimeTest.java
(1 of 2)
Line 10
Lines 13-17
Lines 20-22
Obtain a Calendar with the current date and time
Use the Calendar object in printf statements as the value to be formatted with conversion character t
Use the optional argument index to indicate that all format specifiers in the format string use the first argument

22. Outline
DateTimeTest.java
(2 of 2)
Program output

23. 28.8 Other Conversion Characters
Remaining conversion characters
b or B
boolean or Boolean value
h or H
String representation of an object’s hash code in hexadecimal format %
Percent character n
Platform-specific line separator
\r\n on Windows
\n on UNIX\Linux

24. Common Programming Error 28.2
Trying to print a literal percent character using % rather than %% in the format string might cause a difficult-to-detect logic error. When % appears in a format string, it must be followed by a conversion character in the string. The single percent could accidentally be followed by a legitimate conversion character, thus causing a logic error.

25. Fig. 28.10 | Other conversion specifiers.

26. Outline Print the value of boolean values false and true
OtherConversion.ja va
Lines 9-10
Lines 11-12
Lines 13-14
Line 15
Lines 16-17
Program output
Print the value of boolean values false and true
Associate a String and a null object to %b and %B
Print the string representations of the hash code values for strings “hello” and “Hello”
Print null in uppercase letters
Print the % character in a string and a platform-specific line separator

27. 28.9 Printing with Field Widths and Precisions
Size of field in which data is printed
If width larger than data, default right justified
If field width too small, increases to fit data
Minus sign uses one character position in field
Integer width inserted between % and conversion specifier
E.g., %4d – field width of 4
Can be used with all format specifiers except the line separator (%n)

28. 28.9 Printing with Field Widths and Precisions (Cont.)
Meaning varies depending on data type
Floating point
Number of digits to appear after decimal (e or E and f)
Maximum number of significant digits (g or G)
Strings
Maximum number of characters to be written from string
Format
Use a dot (.) then precision number after %
e.g., %.3f

29. 28.9 Printing with Field Widths and Precisions (Cont.)
Field width and precision
Can both be specified
%width.precision
%5.3f
Negative field width – left justified
Positive field width – right justified
Precision must be positive
Example:
printf( "%9.3f", );

30. Common Programming Error 28.3
Not providing a sufficiently large field width to handle a value to be printed can off­set other data being printed and produce confusing outputs. Know your data!

31. Outline Print positive numbers with field width
FieldWidthTest.jav a
Lines 8-12
Lines 14-18
Program output
Print positive numbers with field width
Print negative numbers with field width

32. Outline
PrecisionTest.java
Line 11
Line 14
Program output
Print same floating-point number with same precision but different conversion character
Print string with precision

33. 28.10 Using Flags in the printf Format String
Supplement formatting capabilities
Place flag immediately to the right of percent sign
Several flags may be combined

34. Fig. 28.14 | Format string flags.

35. Outline
MinusFlagTest.java
Line 10
Lines 11-12
Program output
Right justify a string, an integer, a character and a floating-point number
left justify a string, an integer, a character and a floating-point number

36. Outline Print a positive number with a plus sign PlusFlagTest.java
Program output
Print a positive number with a plus sign

37. Outline Prefix a space to the positive number with the space flag
SpaceFlagTest.java
Line 8
Program output
Prefix a space to the positive number with the space flag

38. Outline
PoundFlagTest.java
Lines 10-11
Program output
Use the # flag to prefix 0 to the octal value and 0x to the hexadecimal value

39. Outline
ZeroFlagTest.java
Line 8
Line 9
Line 10
Program output
Combine the + flag and the 0 flag print 452 in a field of width 9 with a + sign and leading zeros
Print 452 in a field of width 9 using only the 0 flag
Print 452 in a field of width 9 using only the space flag

40. Outline
CommaFlagTest.java
Lines 8-10
Program output
Use the comma flag to display a decimal and a floating-point number with the thousands separator

41. Outline Enclose negative numbers in parentheses using the ( flag
ParenthesesFlagTes t.java
Lines 8-10
Program output
Enclose negative numbers in parentheses using the ( flag

42. 28.11 Printing with Argument Indices
Argument index
Optional decimal integer followed by a $ sign
Indicate the position of the argument in the argument list
E.g., 1$ -- first argument
Usage
Reorder the output
Avoid duplicating arguments

43. Outline
ArgumentIndexTest
Lines 11-13
Program output
Print arguments in the argument list in reverse order using the argument index

44. 28.12 Printing Literals and Escape Sequences
Most characters can be printed
Certain "problem" characters, such as the quotation mark (")
Must be represented by escape sequences
Represented by a backslash \ followed by an escape character

45. Common Programming Error 28.4
Attempting to print as literal data in a printf statement a double quote or backslash character without preceding that character with a backslash to form a proper escape sequence might result in a syntax error.

46. Fig | Escape sequences.

47. 28.13 Formatting Output with Class Formatter
Provides same formatting capabilities as printf
Output formatted data to a specified destination
E.g., a file on disk
By default, Formatter creates a string in memory
String static method format
Create a string in memory without Formatter

48. Outline
FormatterTest.java
Line 11
Line 12
Line 15
Program output
Create a Formatter object using the default constructor, which will build a string in memory
Invoke method format to format the output
Invoke Formatter’s toString method to get the formatted data as a string