Formatted Output

1. 29 • Formatted Output

2. All the news that’s fit to print. Adolph S. Ochs What mad pursuit? What struggle to escape? John Keats Remove not the landmark on the boundary of the fields. Amenehope

3. 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.

4. 29.1   Introduction • 29.2   Streams • 29.3   Formatting Output with printf • 29.4   Printing Integers • 29.5   Printing Floating-Point Numbers • 29.6   Printing Strings and Characters • 29.7   Printing Dates and Times • 29.8   Other Conversion Characters • 29.9   Printing with Field Widths and Precisions • 29.10   Using Flags in the printf Format String • 29.11   Printing with Argument Indices • 29.12   Printing Literals and Escape Sequences • 29.13   Formatting Output with Class Formatter • 29.14   Wrap-Up

5. 29.1 Introduction • Method printf • 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

6. 29.2  Streams • Streams • Sequences of bytes • Can often be redirected • Standard input – keyboard • Standard output – screen • Standard error – screen • More in Chapters 14 and 24

7. 29.3  Formatting Output with printf • 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

8. 29.3  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

9. 29.4  Printing Integers • Integer • Whole number (no decimal point): 25, 0, -9 • Positive, negative, or zero • Only minus sign prints by default • Format • printf(format-string, argument-list); • format-string • Describes the output format • argument-list • Contains the values that corresponding to the format specifiers

10. Fig. 29.1 | Integer conversion characters.

11. Output the integer in octal format Output positive and negative integers Output the integer in hexadecimal format Output the integer in hexadecimal format with capital letters

12. 29.5  Printing Floating-Point Numbers • Floating Point Numbers • Have a decimal point (33.5) • Computerized scientific notation (exponential notation) • 150.4582 is 1.504582 x 10² in scientific • 150.4582 is 1.504582e+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

13. Fig. 29.3 | Floating-point conversion characters.

14. 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

15. 29.6  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

16. Common Programming Error 29.1 • Using %c to print a string causes an IllegalFormatConversionException—a string cannot be converted to a character.

17. 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

18. 29.7  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

19. Fig. 29.6 | Date and time composition conversion suffix characters.

20. Fig. 29.7 | Date formatting conversion suffix characters.

21. Fig. 29.8 | Time formatting conversion suffix characters.

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

24. 29.8 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

25. Common Programming Error 29.2 • 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.

26. Fig. 29.10 | Other conversion specifiers.

27. Print the value of boolean values false and true Associate a String and a null object to %b and %B Print null in uppercase letters Print the string representations of the hash code values for strings “hello” and “Hello” Print the % character in a string and a platform-specific line separator

28. 29.9  Printing with Field Widths and Precisions • Field width • Size of field in which data is displayed • 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)

29. 29.9  Printing with Field Widths and Precisions (Cont.) • Precision • 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

30. 29.9  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", 123.456789 );

31. Common Programming Error 29.3 • 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!

32. Print positive numbers with field width Print negative numbers with field width

33. Print same floating-point number with same precision but different conversion character Print string with precision

34. 29.10 Using Flags in the printf Format String • Flags • Supplement formatting capabilities • Place flag immediately to the right of percent sign • Several flags may be combined

35. Fig. 29.14 | Format string flags.

36. 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

37. Print a positive number with a plus sign

38. Prefix a space to the positive number with the space flag

39. Use the # flag to prefix 0 to the octal value and 0x to the hexadecimal value

40. 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

41. Use the comma flag to display a decimal and a floating-point number with the thousands separator

42. Enclose negative numbers in parentheses using the ( flag Outline • ParenthesesFlagTest.java • Lines 8-10 • Program output

43. 29.11 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

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

45. 29.12 Printing Literals and Escape Sequences • Printing Literals • 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

46. Common Programming Error 29.4 • 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.

47. Fig. 29.23 | Escape sequences.

48. 29.13 Formatting Output with Class Formatter • 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 • Stringstatic method format • Create a string in memory without Formatter

49. 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