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Formatters and Java Print Streams


Last week, we discussed Java print streams, concluding with the format method and formatter objects. This week, we pick up from where we left off. This is the second part of a three-part sereis. It is excerpted from chapter seven of Java I/O, Second Edition, written by Elliotte Rusty Harold (O'Reilly, 2006; ISBN: 0596527500). Copyright © 2006 O'Reilly Media, Inc. All rights reserved. Used with permission from the publisher. Available from booksellers or direct from O'Reilly Media.

Author Info:
By: O'Reilly Media
Rating: 4 stars4 stars4 stars4 stars4 stars / 8
June 21, 2007
TABLE OF CONTENTS:
  1. · Formatters and Java Print Streams
  2. · Character Sets
  3. · Locales
  4. · Format Specifiers
  5. · Floating-point conversions

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Formatters and Java Print Streams - Floating-point conversions
(Page 5 of 5 )

Floating-point conversions can be applied to all floating-point types: float and double, the type-wrapper classesFloatandDouble, andjava.math.BigDecimal. These conversions are:

%f
   A regular base-10 decimal number, such as 3.141593

%e
   A decimal number in scientific notation with a
   lowercase e, such as 3.141593e+00

%E
   A decimal number in scientific notation with an
   uppercase E, such as 3.141593E+00

%g
   A decimal number formatted in either regular or
   scientific notation, depending on its size and
   precision, with a lowercase e if scientific notation is
   used

%G
   A decimal number formatted in either regular or
   scientific notation, depending on its size and
   precision, with an uppercase E if scientific notation is
   used

%a
   A lowercase hexadecimal floating-point number, such
  as 0x1.921fb54442d18p1

%A
   An uppercase hexadecimal floating-point number,
   such as 0X1.921FB54442D18P1

Surprisingly, you cannot use these conversions on integer types such asintorBigDecimal. Java will not automatically promote the integer type to a floating-point type when formatting. If you try to use them, it throws anIllegalFormatConversionException.

Example 7-2 prints π in all of these formats.

Example 7-2.  Floating-point format specifiers

public class FloatingPointFormatExample {

  public static void main(String[] args){
    System.out.printf("Decimal:      %f\n", Math.PI);
    System.out.printf("Scientific notation: %e\n", Math.PI);
    System.out.printf("Scientific notation: %E\n", Math.PI);
    System.out.printf("Decimal/Scientific: %g\n", Math.PI);
    System.out.printf("Decimal/Scientific: %G\n", Math.PI);
    System.out.printf("Lowercase Hexadecimal: %a\n", Math.PI);
    System.out.printf("Uppercase Hexadecimal: %A\n", Math.PI);
 
}
}

Here’s the output:

  Decimal:               3.141593
  Scientific notation:   3.141593e+00
  Scientific notation:   3.141593E+00
  Decimal/Scientific:    3.14159
  Decimal/Scientific:    3.14159
  Lowercase Hexadecimal: 0x1.921fb54442d18p1
  Uppercase Hexadecimal: 0X1.921FB54442D18P1

Please check back next week for the conclusion to this article.


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