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<!-- $Revision: 937893 $ $Date: 2010-04-25 23:42:47 +0200 (dim. 25 avril 2010) $ -->
<document url="fraction.html">
  <properties>
    <title>The Commons Math User Guide - Fractions</title>
  </properties>
  <body>
    <section name="9 Fractions">
      <subsection name="9.1 Overview" href="overview">
        <p>
          The fraction packages provides a fraction number type as well as
          fraction number formatting.
        </p>
      </subsection>
      <subsection name="9.2 Fraction Numbers" href="fraction">
        <p>
          <a href="../apidocs/org/apache/commons/math/fraction/Fraction.html">
          Fraction</a> and <a href="../apidocs/org/apache/commons/math/fraction/BigFraction.html">
          BigFraction</a> provide fraction number type that forms the basis for
          the fraction functionality found in Commons-Math. The former one can be
          used for fractions whose numerators and denominators are small enough
          to fit in an int (taking care of intermediate values) while the second
          class should be used when there is a risk the numerator and denominator
          grow very large.
        </p>
        <p>
          A fraction number, can be built from two integer arguments representing numerator
          and denominator or from a double which will be approximated:
          <source>Fraction f = new Fraction(1, 3); // 1 / 3
Fraction g = new Fraction(0.25); // 1 / 4</source>
        </p>
        <p>
          Of special note with fraction construction, when a fraction is created it is always reduced to lowest terms.
        </p>
        <p>
          The <code>Fraction</code> class provides many unary and binary
          fraction operations.  These operations provide the means to add,
          subtract, multiple and, divide fractions along with other functions similar to the real number functions found in
          <code>java.math.BigDecimal</code>:
          <source>Fraction lhs = new Fraction(1, 3);
Fraction rhs = new Fraction(2, 5);

Fraction answer = lhs.add(rhs);     // add two fractions
        answer = lhs.subtract(rhs); // subtract two fractions
        answer = lhs.abs();         // absolute value
        answer = lhs.reciprocal();  // reciprocal of lhs</source>
        </p>
        <p>
          Like fraction construction, for each of the fraction functions, the resulting fraction is reduced to lowest terms.
        </p>
      </subsection>
      <subsection name="9.3 Fraction Formatting and Parsing" href="formatting">
        <p>
          <code>Fraction</code> instances can be converted to and from strings
          using the<a href="../apidocs/org/apache/commons/math/fraction/FractionFormat.html">
          FractionFormat</a> class. <code>FractionFormat</code> is a
          <code>java.text.Format</code> extension and, as such, is used like other
          formatting objects (e.g. <code>java.text.SimpleDateFormat</code>):
          <source>FractionFormat format = new FractionFormat(); // default format
Fraction f = new Fraction(2, 4);
String s = format.format(f); // s contains "1 / 2", note the reduced fraction</source>
        </p>
        <p>
          To customize the formatting output, one or two
          <code>java.text.NumberFormat</code> instances can be used to construct
          a <code>FractionFormat</code>.  These number formats control the
          formatting of the numerator and denominator of the fraction:
          <source>NumberFormat nf = NumberFormat.getInstance(Locale.FRANCE);
// create fraction format with custom number format
// when one number format is used, both numerator and
// denominator are formatted the same
FractionFormat format = new FractionFormat(nf);
Fraction f = new Fraction(2000, 3333);
String s = format.format(c); // s contains "2.000 / 3.333"

NumberFormat nf2 = NumberFormat.getInstance(Locale.US);
// create fraction format with custom number formats
format = new FractionFormat(nf, nf2);
s = format.format(f); // s contains "2.000 / 3,333"</source>
        </p>
        <p>
          Formatting's inverse operation, parsing, can also be performed by
          <code>FractionFormat</code>.  To parse a fraction from a string,
          simply call the <code>parse</code> method:
          <source>FractionFormat ff = new FractionFormat();
Fraction f = ff.parse("-10 / 21");</source>
        </p>
      </subsection>
    </section>
  </body>
</document>
