1.  2005 Pearson Education, Inc. All rights reserved. 1 28 Formatted Output

2.  2005 Pearson Education, Inc. All rights reserved. 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.  2005 Pearson Education, Inc. All rights reserved. 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.  2005 Pearson Education, Inc. All rights reserved. 4 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

5.  2005 Pearson Education, Inc. All rights reserved. 5 28.1 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.  2005 Pearson Education, Inc. All rights reserved. 6 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

7.  2005 Pearson Education, Inc. All rights reserved. 7 28.3 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.  2005 Pearson Education, Inc. All rights reserved. 8 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

9.  2005 Pearson Education, Inc. All rights reserved. 9 28.4 Printing Integers Integer – 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

10.  2005 Pearson Education, Inc. All rights reserved. 10 Fig. 28.1 | Integer conversion characters.

11.  2005 Pearson Education, Inc. All rights reserved. 11 Outline IntegerConversionT est.java Lines 8-10 Line 11 Line 12 Line 13 Program output Output the integer in octal formatOutput the integer in hexadecimal formatOutput the integer in hexadecimal format with capital letters Output positive and negative integers

12.  2005 Pearson Education, Inc. All rights reserved. 12 28.5 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 10 7

13.  2005 Pearson Education, Inc. All rights reserved. 13 Fig. 28.3 | Floating-point conversion characters.

14.  2005 Pearson Education, Inc. All rights reserved. 14 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

15.  2005 Pearson Education, Inc. All rights reserved. 15 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

16.  2005 Pearson Education, Inc. All rights reserved. 16 Common Programming Error 28.1 Using % c to print a string causes an IllegalFormatConversionException —a string cannot be converted to a character.

17.  2005 Pearson Education, Inc. All rights reserved. 17 Outline 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

18.  2005 Pearson Education, Inc. All rights reserved. 18 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

19.  2005 Pearson Education, Inc. All rights reserved. 19 Fig. 28.6 | Date and time composition conversion suffix characters.

20.  2005 Pearson Education, Inc. All rights reserved. 20 Fig. 28.7 | Date formatting conversion suffix characters.

21.  2005 Pearson Education, Inc. All rights reserved. 21 Fig. 28.8 | Time formatting conversion suffix characters.

22.  2005 Pearson Education, Inc. All rights reserved. 22 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 optional argument index to indicate that all format specifiers in the format string use the first argument Use the Calendar object in printf statements as the value to be formatted with conversion character t

23.  2005 Pearson Education, Inc. All rights reserved. 23 Outline DateTimeTest.java (2 of 2) Program output

24.  2005 Pearson Education, Inc. All rights reserved. 24 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

25.  2005 Pearson Education, Inc. All rights reserved. 25 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.

26.  2005 Pearson Education, Inc. All rights reserved. 26 Fig. 28.10 | Other conversion specifiers.

27.  2005 Pearson Education, Inc. All rights reserved. 27 Outline 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

28.  2005 Pearson Education, Inc. All rights reserved. 28 28.9 Printing with Field Widths and Precisions Field width – 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 )

29.  2005 Pearson Education, Inc. All rights reserved. 29 28.9 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.  2005 Pearson Education, Inc. All rights reserved. 30 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", 123.456789 );

31.  2005 Pearson Education, Inc. All rights reserved. 31 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!

32.  2005 Pearson Education, Inc. All rights reserved. 32 Outline FieldWidthTest.jav a Lines 8-12 Lines 14-18 Program output Print positive numbers with field width Print negative numbers with field width

33.  2005 Pearson Education, Inc. All rights reserved. 33 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

34.  2005 Pearson Education, Inc. All rights reserved. 34 28.10 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.  2005 Pearson Education, Inc. All rights reserved. 35 Fig. 28.14 | Format string flags.

36.  2005 Pearson Education, Inc. All rights reserved. 36 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

37.  2005 Pearson Education, Inc. All rights reserved. 37 Outline PlusFlagTest.java Line 9 Program output Print a positive number with a plus sign

38.  2005 Pearson Education, Inc. All rights reserved. 38 Outline SpaceFlagTest.java Line 8 Program output Prefix a space to the positive number with the space flag

39.  2005 Pearson Education, Inc. All rights reserved. 39 Outline PoundFlagTest.java Lines 10-11 Program output Use the # flag to prefix 0 to the octal value and 0x to the hexadecimal value

40.  2005 Pearson Education, Inc. All rights reserved. 40 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

41.  2005 Pearson Education, Inc. All rights reserved. 41 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

42.  2005 Pearson Education, Inc. All rights reserved. 42 Outline ParenthesesFlagTes t.java Lines 8-10 Program output Enclose negative numbers in parentheses using the ( flag

43.  2005 Pearson Education, Inc. All rights reserved. 43 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

44.  2005 Pearson Education, Inc. All rights reserved. 44 Outline ArgumentIndexTest Lines 11-13 Program output Print arguments in the argument list in reverse order using the argument index

45.  2005 Pearson Education, Inc. All rights reserved. 45 28.12 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.  2005 Pearson Education, Inc. All rights reserved. 46 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.

47.  2005 Pearson Education, Inc. All rights reserved. 47 Fig. 28.23 | Escape sequences.

48.  2005 Pearson Education, Inc. All rights reserved. 48 28.13 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 String static method format – Create a string in memory without Formatter

49.  2005 Pearson Education, Inc. All rights reserved. 49 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