Formatters and Java Print Streams - Floating-point conversions
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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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 This article is excerpted from chapter seven of Java I/O, Second Edition, written by Elliotte Rusty Harold (O'Reilly, 2006; ISBN: 0596527500). Check it out today at your favorite bookstore. Buy this book now.
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