simplificar - ¿La mejor forma de representar una fracción en Java?

simplificar fracciones python

Question

Estoy tratando de trabajar con fractions en Java.

Quiero implementar funciones aritméticas. Para esto, primero requeriré una forma de normalizar las funciones. Sé que no puedo agregar 1/6 y 1/2 hasta que tenga un denominador común. Tendré que agregar 1/6 y 3/6. Un enfoque ingenuo me haría agregar 2/12 y 6/12 y luego reducir. ¿Cómo puedo lograr un denominador común con la pena de menor rendimiento? ¿Qué algoritmo es mejor para esto?

Versión 8 (gracias a hstoerr ):

Las mejoras incluyen:

• el método equals () ahora es consistente con el método compareTo ()

final class Fraction extends Number {
    private int numerator;
    private int denominator;

    public Fraction(int numerator, int denominator) {
        if(denominator == 0) {
            throw new IllegalArgumentException("denominator is zero");
        }
        if(denominator < 0) {
            numerator *= -1;
            denominator *= -1;
        }
        this.numerator = numerator;
        this.denominator = denominator;
    }

    public Fraction(int numerator) {
        this.numerator = numerator;
        this.denominator = 1;
    }

    public int getNumerator() {
        return this.numerator;
    }

    public int getDenominator() {
        return this.denominator;
    }

    public byte byteValue() {
        return (byte) this.doubleValue();
    }

    public double doubleValue() {
        return ((double) numerator)/((double) denominator);
    }

    public float floatValue() {
        return (float) this.doubleValue();
    }

    public int intValue() {
        return (int) this.doubleValue();
    }

    public long longValue() {
        return (long) this.doubleValue();
    }

    public short shortValue() {
        return (short) this.doubleValue();
    }

    public boolean equals(Fraction frac) {
        return this.compareTo(frac) == 0;
    }

    public int compareTo(Fraction frac) {
        long t = this.getNumerator() * frac.getDenominator();
        long f = frac.getNumerator() * this.getDenominator();
        int result = 0;
        if(t>f) {
            result = 1;
        }
        else if(f>t) {
            result = -1;
        }
        return result;
    }
}

He eliminado todas las versiones anteriores. Mi agradecimiento a:

• Dave Ray
• cletus
• duffymo
• James
• Milhous
• Oscar Reyes
• Jason S
• Francisco Canedo
• Programador fuera de la ley
• Beska

Answer 1

Estoy tratando de trabajar con fracciones adecuadas en Java.

Apache Commons Math ha tenido una clase commons.apache.org/math/userguide/fraction.html durante bastante tiempo. La mayoría de las veces la respuesta es: "¡Ojalá Java tuviera algo como X en la biblioteca principal!" se puede encontrar bajo el paraguas de la biblioteca de Apache Commons .

Answer 2

Specifically : Is there a better way to handle being passed a zero denominator? Setting the denominator to 1 is feels mighty arbitrary. How can I do this right?

I would say throw a ArithmeticException for divide by zero, since that''s really what''s happening:

public Fraction(int numerator, int denominator) {
    if(denominator == 0)
        throw new ArithmeticException("Divide by zero.");
    this.numerator = numerator;
    this.denominator = denominator;
}

Instead of "Divide by zero.", you might want to make the message say "Divide by zero: Denominator for Fraction is zero."

Answer 3

I will need to order them from smallest to largest, so eventually I will need to represent them as a double also

Not strictly necessary. (In fact if you want to handle equality correctly, don''t rely on double to work properly.) If b*d is positive, a/b < c/d if ad < bc. If there are negative integers involved, that can be handled appropriately...

I might rewrite as:

public int compareTo(Fraction frac)
{
    // we are comparing this=a/b with frac=c/d 
    // by multiplying both sides by bd.
    // If bd is positive, then a/b < c/d <=> ad < bc.
    // If bd is negative, then a/b < c/d <=> ad > bc.
    // If bd is 0, then you''ve got other problems (either b=0 or d=0)
    int d = frac.getDenominator();
    long ad = (long)this.numerator * d;
    long bc = (long)this.denominator * frac.getNumerator();
    long diff = ((long)d*this.denominator > 0) ? (ad-bc) : (bc-ad);
    return (diff > 0 ? 1 : (diff < 0 ? -1 : 0));
}

The use of long here is to ensure there''s not an overflow if you multiply two large int s. handle If you can guarantee that the denominator is always nonnegative (if it''s negative, just negate both numerator and denominator), then you can get rid of having to check whether b*d is positive and save a few steps. I''m not sure what behavior you''re looking for with zero denominator.

Not sure how performance compares to using doubles to compare. (that is, if you care about performance that much) Here''s a test method I used to check. (Appears to work properly.)

public static void main(String[] args)
{
    int a = Integer.parseInt(args[0]);
    int b = Integer.parseInt(args[1]);
    int c = Integer.parseInt(args[2]);
    int d = Integer.parseInt(args[3]);
    Fraction f1 = new Fraction(a,b); 
    Fraction f2 = new Fraction(c,d);
    int rel = f1.compareTo(f2);
    String relstr = "<=>";
    System.out.println(a+"/"+b+" "+relstr.charAt(rel+1)+" "+c+"/"+d);
}

(ps you might consider restructuring to implement Comparable or Comparator for your class.)

Answer 4

¡Por favor haz que sea un tipo inmutable! El valor de una fracción no cambia: una mitad no se convierte en una tercera, por ejemplo. En lugar de setDenominator, podrías tener withDenominator que devuelve una nueva fracción que tiene el mismo numerador pero el denominador especificado.

La vida es mucho más fácil con tipos inmutables.

Anular Iguales y Hashcode también sería sensato, por lo que se puede usar en mapas y conjuntos. Los puntos de Outlaw Programmer acerca de los operadores aritméticos y el formato de cadenas también son buenos.

Como guía general, eche un vistazo a BigInteger y BigDecimal. No están haciendo lo mismo, pero son lo suficientemente similares como para darte buenas ideas.

Answer 5

Bueno, por un lado, me deshace de los organismos que crean y hace que las fracciones sean inmutables.

Probablemente también quiera métodos para sumar, restar, etc., y quizás alguna forma de obtener la representación en varios formatos de Cadena.

EDITAR: Probablemente marcaría los campos como ''final'' para señalar mi intención, pero supongo que no es gran cosa ...

Answer 6

Da la casualidad de que escribí una clase de BigFraction no hace mucho tiempo, para problemas del Proyecto Euler . Mantiene un numerador y denominador BigInteger, por lo que nunca se desbordará. Pero será un poco lento para muchas operaciones que usted sabe que nunca se desbordarán ... de todos modos, úselas si lo desea. He estado muriendo por mostrar esto de alguna manera. :)

Editar : La versión más reciente y mejor de este código, incluidas las pruebas unitarias, ahora está alojada en GitHub y también está disponible a través de Maven Central . Dejo mi código original aquí para que esta respuesta no sea solo un enlace ...

import java.math.*;

/**
 * Arbitrary-precision fractions, utilizing BigIntegers for numerator and
 * denominator.  Fraction is always kept in lowest terms.  Fraction is
 * immutable, and guaranteed not to have a null numerator or denominator.
 * Denominator will always be positive (so sign is carried by numerator,
 * and a zero-denominator is impossible).
 */
public final class BigFraction extends Number implements Comparable<BigFraction>
{
  private static final long serialVersionUID = 1L; //because Number is Serializable
  private final BigInteger numerator;
  private final BigInteger denominator;

  public final static BigFraction ZERO = new BigFraction(BigInteger.ZERO, BigInteger.ONE, true);
  public final static BigFraction ONE = new BigFraction(BigInteger.ONE, BigInteger.ONE, true);

  /**
   * Constructs a BigFraction with given numerator and denominator.  Fraction
   * will be reduced to lowest terms.  If fraction is negative, negative sign will
   * be carried on numerator, regardless of how the values were passed in.
   */
  public BigFraction(BigInteger numerator, BigInteger denominator)
  {
    if(numerator == null)
      throw new IllegalArgumentException("Numerator is null");
    if(denominator == null)
      throw new IllegalArgumentException("Denominator is null");
    if(denominator.equals(BigInteger.ZERO))
      throw new ArithmeticException("Divide by zero.");

    //only numerator should be negative.
    if(denominator.signum() < 0)
    {
      numerator = numerator.negate();
      denominator = denominator.negate();
    }

    //create a reduced fraction
    BigInteger gcd = numerator.gcd(denominator);
    this.numerator = numerator.divide(gcd);
    this.denominator = denominator.divide(gcd);
  }

  /**
   * Constructs a BigFraction from a whole number.
   */
  public BigFraction(BigInteger numerator)
  {
    this(numerator, BigInteger.ONE, true);
  }

  public BigFraction(long numerator, long denominator)
  {
    this(BigInteger.valueOf(numerator), BigInteger.valueOf(denominator));
  }

  public BigFraction(long numerator)
  {
    this(BigInteger.valueOf(numerator), BigInteger.ONE, true);
  }

  /**
   * Constructs a BigFraction from a floating-point number.
   * 
   * Warning: round-off error in IEEE floating point numbers can result
   * in answers that are unexpected.  For example, 
   *     System.out.println(new BigFraction(1.1))
   * will print:
   *     2476979795053773/2251799813685248
   * 
   * This is because 1.1 cannot be expressed exactly in binary form.  The
   * given fraction is exactly equal to the internal representation of
   * the double-precision floating-point number.  (Which, for 1.1, is:
   * (-1)^0 * 2^0 * (1 + 0x199999999999aL / 0x10000000000000L).)
   * 
   * NOTE: In many cases, BigFraction(Double.toString(d)) may give a result
   * closer to what the user expects.
   */
  public BigFraction(double d)
  {
    if(Double.isInfinite(d))
      throw new IllegalArgumentException("double val is infinite");
    if(Double.isNaN(d))
      throw new IllegalArgumentException("double val is NaN");

    //special case - math below won''t work right for 0.0 or -0.0
    if(d == 0)
    {
      numerator = BigInteger.ZERO;
      denominator = BigInteger.ONE;
      return;
    }

    final long bits = Double.doubleToLongBits(d);
    final int sign = (int)(bits >> 63) & 0x1;
    final int exponent = ((int)(bits >> 52) & 0x7ff) - 0x3ff;
    final long mantissa = bits & 0xfffffffffffffL;

    //number is (-1)^sign * 2^(exponent) * 1.mantissa
    BigInteger tmpNumerator = BigInteger.valueOf(sign==0 ? 1 : -1);
    BigInteger tmpDenominator = BigInteger.ONE;

    //use shortcut: 2^x == 1 << x.  if x is negative, shift the denominator
    if(exponent >= 0)
      tmpNumerator = tmpNumerator.multiply(BigInteger.ONE.shiftLeft(exponent));
    else
      tmpDenominator = tmpDenominator.multiply(BigInteger.ONE.shiftLeft(-exponent));

    //1.mantissa == 1 + mantissa/2^52 == (2^52 + mantissa)/2^52
    tmpDenominator = tmpDenominator.multiply(BigInteger.valueOf(0x10000000000000L));
    tmpNumerator = tmpNumerator.multiply(BigInteger.valueOf(0x10000000000000L + mantissa));

    BigInteger gcd = tmpNumerator.gcd(tmpDenominator);
    numerator = tmpNumerator.divide(gcd);
    denominator = tmpDenominator.divide(gcd);
  }

  /**
   * Constructs a BigFraction from two floating-point numbers.
   * 
   * Warning: round-off error in IEEE floating point numbers can result
   * in answers that are unexpected.  See BigFraction(double) for more
   * information.
   * 
   * NOTE: In many cases, BigFraction(Double.toString(numerator) + "/" + Double.toString(denominator))
   * may give a result closer to what the user expects.
   */
  public BigFraction(double numerator, double denominator)
  {
    if(denominator == 0)
      throw new ArithmeticException("Divide by zero.");

    BigFraction tmp = new BigFraction(numerator).divide(new BigFraction(denominator));
    this.numerator = tmp.numerator;
    this.denominator = tmp.denominator;
  }

  /**
   * Constructs a new BigFraction from the given BigDecimal object.
   */
  public BigFraction(BigDecimal d)
  {
    this(d.scale() < 0 ? d.unscaledValue().multiply(BigInteger.TEN.pow(-d.scale())) : d.unscaledValue(),
         d.scale() < 0 ? BigInteger.ONE                                             : BigInteger.TEN.pow(d.scale()));
  }

  public BigFraction(BigDecimal numerator, BigDecimal denominator)
  {
    if(denominator.equals(BigDecimal.ZERO))
      throw new ArithmeticException("Divide by zero.");

    BigFraction tmp = new BigFraction(numerator).divide(new BigFraction(denominator));
    this.numerator = tmp.numerator;
    this.denominator = tmp.denominator;
  }

  /**
   * Constructs a BigFraction from a String.  Expected format is numerator/denominator,
   * but /denominator part is optional.  Either numerator or denominator may be a floating-
   * point decimal number, which in the same format as a parameter to the
   * <code>BigDecimal(String)</code> constructor.
   * 
   * @throws NumberFormatException  if the string cannot be properly parsed.
   */
  public BigFraction(String s)
  {
    int slashPos = s.indexOf(''/'');
    if(slashPos < 0)
    {
      BigFraction res = new BigFraction(new BigDecimal(s));
      this.numerator = res.numerator;
      this.denominator = res.denominator;
    }
    else
    {
      BigDecimal num = new BigDecimal(s.substring(0, slashPos));
      BigDecimal den = new BigDecimal(s.substring(slashPos+1, s.length()));
      BigFraction res = new BigFraction(num, den);
      this.numerator = res.numerator;
      this.denominator = res.denominator;
    }
  }

  /**
   * Returns this + f.
   */
  public BigFraction add(BigFraction f)
  {
    if(f == null)
      throw new IllegalArgumentException("Null argument");

    //n1/d1 + n2/d2 = (n1*d2 + d1*n2)/(d1*d2) 
    return new BigFraction(numerator.multiply(f.denominator).add(denominator.multiply(f.numerator)),
                           denominator.multiply(f.denominator));
  }

  /**
   * Returns this + b.
   */
  public BigFraction add(BigInteger b)
  {
    if(b == null)
      throw new IllegalArgumentException("Null argument");

    //n1/d1 + n2 = (n1 + d1*n2)/d1
    return new BigFraction(numerator.add(denominator.multiply(b)),
                           denominator, true);
  }

  /**
   * Returns this + n.
   */
  public BigFraction add(long n)
  {
    return add(BigInteger.valueOf(n));
  }

  /**
   * Returns this - f.
   */
  public BigFraction subtract(BigFraction f)
  {
    if(f == null)
      throw new IllegalArgumentException("Null argument");

    return new BigFraction(numerator.multiply(f.denominator).subtract(denominator.multiply(f.numerator)),
                           denominator.multiply(f.denominator));
  }

  /**
   * Returns this - b.
   */
  public BigFraction subtract(BigInteger b)
  {
    if(b == null)
      throw new IllegalArgumentException("Null argument");

    return new BigFraction(numerator.subtract(denominator.multiply(b)),
                           denominator, true);
  }

  /**
   * Returns this - n.
   */
  public BigFraction subtract(long n)
  {
    return subtract(BigInteger.valueOf(n));
  }

  /**
   * Returns this * f.
   */
  public BigFraction multiply(BigFraction f)
  {
    if(f == null)
      throw new IllegalArgumentException("Null argument");

    return new BigFraction(numerator.multiply(f.numerator), denominator.multiply(f.denominator));
  }

  /**
   * Returns this * b.
   */
  public BigFraction multiply(BigInteger b)
  {
    if(b == null)
      throw new IllegalArgumentException("Null argument");

    return new BigFraction(numerator.multiply(b), denominator);
  }

  /**
   * Returns this * n.
   */
  public BigFraction multiply(long n)
  {
    return multiply(BigInteger.valueOf(n));
  }

  /**
   * Returns this / f.
   */
  public BigFraction divide(BigFraction f)
  {
    if(f == null)
      throw new IllegalArgumentException("Null argument");

    if(f.numerator.equals(BigInteger.ZERO))
      throw new ArithmeticException("Divide by zero");

    return new BigFraction(numerator.multiply(f.denominator), denominator.multiply(f.numerator));
  }

  /**
   * Returns this / b.
   */
  public BigFraction divide(BigInteger b)
  {
    if(b == null)
      throw new IllegalArgumentException("Null argument");

    if(b.equals(BigInteger.ZERO))
      throw new ArithmeticException("Divide by zero");

    return new BigFraction(numerator, denominator.multiply(b));
  }

  /**
   * Returns this / n.
   */
  public BigFraction divide(long n)
  {
    return divide(BigInteger.valueOf(n));
  }

  /**
   * Returns this^exponent.
   */
  public BigFraction pow(int exponent)
  {
    if(exponent == 0)
      return BigFraction.ONE;
    else if (exponent == 1)
      return this;
    else if (exponent < 0)
      return new BigFraction(denominator.pow(-exponent), numerator.pow(-exponent), true);
    else
      return new BigFraction(numerator.pow(exponent), denominator.pow(exponent), true);
  }

  /**
   * Returns 1/this.
   */
  public BigFraction reciprocal()
  {
    if(this.numerator.equals(BigInteger.ZERO))
      throw new ArithmeticException("Divide by zero");

    return new BigFraction(denominator, numerator, true);
  }

  /**
   * Returns the complement of this fraction, which is equal to 1 - this.
   * Useful for probabilities/statistics.

   */
  public BigFraction complement()
  {
    return new BigFraction(denominator.subtract(numerator), denominator, true);
  }

  /**
   * Returns -this.
   */
  public BigFraction negate()
  {
    return new BigFraction(numerator.negate(), denominator, true);
  }

  /**
   * Returns -1, 0, or 1, representing the sign of this fraction.
   */
  public int signum()
  {
    return numerator.signum();
  }

  /**
   * Returns the absolute value of this.
   */
  public BigFraction abs()
  {
    return (signum() < 0 ? negate() : this);
  }

  /**
   * Returns a string representation of this, in the form
   * numerator/denominator.
   */
  public String toString()
  {
    return numerator.toString() + "/" + denominator.toString();
  }

  /**
   * Returns if this object is equal to another object.
   */
  public boolean equals(Object o)
  {
    if(!(o instanceof BigFraction))
      return false;

    BigFraction f = (BigFraction)o;
    return numerator.equals(f.numerator) && denominator.equals(f.denominator);
  }

  /**
   * Returns a hash code for this object.
   */
  public int hashCode()
  {
    //using the method generated by Eclipse, but streamlined a bit..
    return (31 + numerator.hashCode())*31 + denominator.hashCode();
  }

  /**
   * Returns a negative, zero, or positive number, indicating if this object
   * is less than, equal to, or greater than f, respectively.
   */
  public int compareTo(BigFraction f)
  {
    if(f == null)
      throw new IllegalArgumentException("Null argument");

    //easy case: this and f have different signs
    if(signum() != f.signum())
      return signum() - f.signum();

    //next easy case: this and f have the same denominator
    if(denominator.equals(f.denominator))
      return numerator.compareTo(f.numerator);

    //not an easy case, so first make the denominators equal then compare the numerators 
    return numerator.multiply(f.denominator).compareTo(denominator.multiply(f.numerator));
  }

  /**
   * Returns the smaller of this and f.
   */
  public BigFraction min(BigFraction f)
  {
    if(f == null)
      throw new IllegalArgumentException("Null argument");

    return (this.compareTo(f) <= 0 ? this : f);
  }

  /**
   * Returns the maximum of this and f.
   */
  public BigFraction max(BigFraction f)
  {
    if(f == null)
      throw new IllegalArgumentException("Null argument");

    return (this.compareTo(f) >= 0 ? this : f);
  }

  /**
   * Returns a positive BigFraction, greater than or equal to zero, and less than one.
   */
  public static BigFraction random()
  {
    return new BigFraction(Math.random());
  }

  public final BigInteger getNumerator() { return numerator; }
  public final BigInteger getDenominator() { return denominator; }

  //implementation of Number class.  may cause overflow.
  public byte   byteValue()   { return (byte) Math.max(Byte.MIN_VALUE,    Math.min(Byte.MAX_VALUE,    longValue())); }
  public short  shortValue()  { return (short)Math.max(Short.MIN_VALUE,   Math.min(Short.MAX_VALUE,   longValue())); }
  public int    intValue()    { return (int)  Math.max(Integer.MIN_VALUE, Math.min(Integer.MAX_VALUE, longValue())); }
  public long   longValue()   { return Math.round(doubleValue()); }
  public float  floatValue()  { return (float)doubleValue(); }
  public double doubleValue() { return toBigDecimal(18).doubleValue(); }

  /**
   * Returns a BigDecimal representation of this fraction.  If possible, the
   * returned value will be exactly equal to the fraction.  If not, the BigDecimal
   * will have a scale large enough to hold the same number of significant figures
   * as both numerator and denominator, or the equivalent of a double-precision
   * number, whichever is more.
   */
  public BigDecimal toBigDecimal()
  {
    //Implementation note:  A fraction can be represented exactly in base-10 iff its
    //denominator is of the form 2^a * 5^b, where a and b are nonnegative integers.
    //(In other words, if there are no prime factors of the denominator except for
    //2 and 5, or if the denominator is 1).  So to determine if this denominator is
    //of this form, continually divide by 2 to get the number of 2''s, and then
    //continually divide by 5 to get the number of 5''s.  Afterward, if the denominator
    //is 1 then there are no other prime factors.

    //Note: number of 2''s is given by the number of trailing 0 bits in the number
    int twos = denominator.getLowestSetBit();
    BigInteger tmpDen = denominator.shiftRight(twos); // x / 2^n === x >> n

    final BigInteger FIVE = BigInteger.valueOf(5);
    int fives = 0;
    BigInteger[] divMod = null;

    //while(tmpDen % 5 == 0) { fives++; tmpDen /= 5; }
    while(BigInteger.ZERO.equals((divMod = tmpDen.divideAndRemainder(FIVE))[1]))
    {
      fives++;
      tmpDen = divMod[0];
    }

    if(BigInteger.ONE.equals(tmpDen))
    {
      //This fraction will terminate in base 10, so it can be represented exactly as
      //a BigDecimal.  We would now like to make the fraction of the form
      //unscaled / 10^scale.  We know that 2^x * 5^x = 10^x, and our denominator is
      //in the form 2^twos * 5^fives.  So use max(twos, fives) as the scale, and
      //multiply the numerator and deminator by the appropriate number of 2''s or 5''s
      //such that the denominator is of the form 2^scale * 5^scale.  (Of course, we
      //only have to actually multiply the numerator, since all we need for the
      //BigDecimal constructor is the scale.
      BigInteger unscaled = numerator;
      int scale = Math.max(twos, fives);

      if(twos < fives)
        unscaled = unscaled.shiftLeft(fives - twos); //x * 2^n === x << n
      else if (fives < twos)
        unscaled = unscaled.multiply(FIVE.pow(twos - fives));

      return new BigDecimal(unscaled, scale);
    }

    //else: this number will repeat infinitely in base-10.  So try to figure out
    //a good number of significant digits.  Start with the number of digits required
    //to represent the numerator and denominator in base-10, which is given by
    //bitLength / log[2](10).  (bitLenth is the number of digits in base-2).
    final double LG10 = 3.321928094887362; //Precomputed ln(10)/ln(2), a.k.a. log[2](10)
    int precision = Math.max(numerator.bitLength(), denominator.bitLength());
    precision = (int)Math.ceil(precision / LG10);

    //If the precision is less than 18 digits, use 18 digits so that the number
    //will be at least as accurate as a cast to a double.  For example, with
    //the fraction 1/3, precision will be 1, giving a result of 0.3.  This is
    //quite a bit different from what a user would expect.
    if(precision < 18)
      precision = 18;

    return toBigDecimal(precision);
  }

  /**
   * Returns a BigDecimal representation of this fraction, with a given precision.
   * @param precision  the number of significant figures to be used in the result.
   */
  public BigDecimal toBigDecimal(int precision)
  {
    return new BigDecimal(numerator).divide(new BigDecimal(denominator), new MathContext(precision, RoundingMode.HALF_EVEN));
  }

  //--------------------------------------------------------------------------
  //  PRIVATE FUNCTIONS
  //--------------------------------------------------------------------------

  /**
   * Private constructor, used when you can be certain that the fraction is already in
   * lowest terms.  No check is done to reduce numerator/denominator.  A check is still
   * done to maintain a positive denominator.
   * 
   * @param throwaway  unused variable, only here to signal to the compiler that this
   *                   constructor should be used.
   */
  private BigFraction(BigInteger numerator, BigInteger denominator, boolean throwaway)
  {
    if(denominator.signum() < 0)
    {
      this.numerator = numerator.negate();
      this.denominator = denominator.negate();
    }
    else
    {
      this.numerator = numerator;
      this.denominator = denominator;
    }
  }

}

Answer 7

A clean up practice that I like is to only have only one return.

 public int compareTo(Fraction frac) {
        int result = 0
        double t = this.doubleValue();
        double f = frac.doubleValue();
        if(t>f) 
           result = 1;
        else if(f>t) 
           result -1;
        return result;
    }

Answer 8

Even though you have the methods compareTo(), if you want to make use of utilities like Collections.sort(), then you should also implement Comparable.

public class Fraction extends Number implements Comparable<Fraction> {
 ...
}

Also, for pretty display I recommend overriding toString()

public String toString() {
    return this.getNumerator() + "/" + this.getDenominator();
}

And finally, I''d make the class public so that you can use it from different packages.

Answer 9

For industry-grade Fraction/Rational implementation, I would implement it so it can represent NaN, positive infinity, negative infinity, and optionally negative zero with operational semantics exactly the same as the IEEE 754 standard states for floating point arithmetics (it also eases the conversion to/from floating point values). Plus, since comparison to zero, one, and the special values above only needs simple, but combined comparison of the numerator and denominator against 0 and 1 - i would add several isXXX and compareToXXX methods for ease of use (eg. eq0() would use numerator == 0 && denominator != 0 behind the scenes instead of letting the client to compare against a zero valued instance). Some statically predefined values (ZERO, ONE, TWO, TEN, ONE_TENTH, NAN, etc.) are also useful, since they appear at several places as constant values. This is the best way IMHO.

Answer 10

I cleaned up cletus'' answer :

• Added Javadoc for all methods.
• Added checks for method preconditions.
• Replaced custom parsing in valueOf(String) with the BigInteger(String) which is both more flexible and faster.

import com.google.common.base.Splitter;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.RoundingMode;
import java.util.List;
import java.util.Objects;
import org.bitbucket.cowwoc.preconditions.Preconditions;

/**
 * A rational fraction, represented by {@code numerator / denominator}.
 * <p>
 * This implementation is based on <a
 * href="https://.com/a/474577/14731">https://.com/a/474577/14731</a>
 * <p>
 * @author Gili Tzabari
 */
public final class BigRational extends Number implements Comparable<BigRational>
{
    private static final long serialVersionUID = 0L;
    public static final BigRational ZERO = new BigRational(BigInteger.ZERO, BigInteger.ONE);
    public static final BigRational ONE = new BigRational(BigInteger.ONE, BigInteger.ONE);

    /**
     * Ensures the fraction the denominator is positive and optionally divides the numerator and
     * denominator by the greatest common factor.
     * <p>
     * @param numerator   a numerator
     * @param denominator a denominator
     * @param checkGcd    true if the numerator and denominator should be divided by the greatest
     *                    common factor
     * @return the canonical representation of the rational fraction
     */
    private static BigRational canonical(BigInteger numerator, BigInteger denominator,
        boolean checkGcd)
    {
        assert (numerator != null);
        assert (denominator != null);
        if (denominator.signum() == 0)
            throw new IllegalArgumentException("denominator is zero");
        if (numerator.signum() == 0)
            return ZERO;
        BigInteger newNumerator = numerator;
        BigInteger newDenominator = denominator;
        if (newDenominator.signum() < 0)
        {
            newNumerator = newNumerator.negate();
            newDenominator = newDenominator.negate();
        }
        if (checkGcd)
        {
            BigInteger gcd = newNumerator.gcd(newDenominator);
            if (!gcd.equals(BigInteger.ONE))
            {
                newNumerator = newNumerator.divide(gcd);
                newDenominator = newDenominator.divide(gcd);
            }
        }
        return new BigRational(newNumerator, newDenominator);
    }

    /**
     * @param numerator   a numerator
     * @param denominator a denominator
     * @return a BigRational having value {@code numerator / denominator}
     * @throws NullPointerException if numerator or denominator are null
     */
    public static BigRational valueOf(BigInteger numerator, BigInteger denominator)
    {
        Preconditions.requireThat(numerator, "numerator").isNotNull();
        Preconditions.requireThat(denominator, "denominator").isNotNull();
        return canonical(numerator, denominator, true);
    }

    /**
     * @param numerator   a numerator
     * @param denominator a denominator
     * @return a BigRational having value {@code numerator / denominator}
     */
    public static BigRational valueOf(long numerator, long denominator)
    {
        BigInteger bigNumerator = BigInteger.valueOf(numerator);
        BigInteger bigDenominator = BigInteger.valueOf(denominator);
        return canonical(bigNumerator, bigDenominator, true);
    }

    /**
     * @param value the parameter value
     * @param name  the parameter name
     * @return the BigInteger representation of the parameter
     * @throws NumberFormatException if value is not a valid representation of BigInteger
     */
    private static BigInteger requireBigInteger(String value, String name)
        throws NumberFormatException
    {
        try
        {
            return new BigInteger(value);
        }
        catch (NumberFormatException e)
        {
            throw (NumberFormatException) new NumberFormatException("Invalid " + name + ": " + value).
                initCause(e);
        }
    }

    /**
     * @param numerator   a numerator
     * @param denominator a denominator
     * @return a BigRational having value {@code numerator / denominator}
     * @throws NullPointerException     if numerator or denominator are null
     * @throws IllegalArgumentException if numerator or denominator are empty
     * @throws NumberFormatException    if numerator or denominator are not a valid representation of
     *                                  BigDecimal
     */
    public static BigRational valueOf(String numerator, String denominator)
        throws NullPointerException, IllegalArgumentException, NumberFormatException
    {
        Preconditions.requireThat(numerator, "numerator").isNotNull().isNotEmpty();
        Preconditions.requireThat(denominator, "denominator").isNotNull().isNotEmpty();
        BigInteger bigNumerator = requireBigInteger(numerator, "numerator");
        BigInteger bigDenominator = requireBigInteger(denominator, "denominator");
        return canonical(bigNumerator, bigDenominator, true);
    }

    /**
     * @param value a string representation of a rational fraction (e.g. "12.34e5" or "3/4")
     * @return a BigRational representation of the String
     * @throws NullPointerException     if value is null
     * @throws IllegalArgumentException if value is empty
     * @throws NumberFormatException    if numerator or denominator are not a valid representation of
     *                                  BigDecimal
     */
    public static BigRational valueOf(String value)
        throws NullPointerException, IllegalArgumentException, NumberFormatException
    {
        Preconditions.requireThat(value, "value").isNotNull().isNotEmpty();
        List<String> fractionParts = Splitter.on(''/'').splitToList(value);
        if (fractionParts.size() == 1)
            return valueOfRational(value);
        if (fractionParts.size() == 2)
            return BigRational.valueOf(fractionParts.get(0), fractionParts.get(1));
        throw new IllegalArgumentException("Too many slashes: " + value);
    }

    /**
     * @param value a string representation of a rational fraction (e.g. "12.34e5")
     * @return a BigRational representation of the String
     * @throws NullPointerException     if value is null
     * @throws IllegalArgumentException if value is empty
     * @throws NumberFormatException    if numerator or denominator are not a valid representation of
     *                                  BigDecimal
     */
    private static BigRational valueOfRational(String value)
        throws NullPointerException, IllegalArgumentException, NumberFormatException
    {
        Preconditions.requireThat(value, "value").isNotNull().isNotEmpty();
        BigDecimal bigDecimal = new BigDecimal(value);
        int scale = bigDecimal.scale();
        BigInteger numerator = bigDecimal.unscaledValue();
        BigInteger denominator;
        if (scale > 0)
            denominator = BigInteger.TEN.pow(scale);
        else
        {
            numerator = numerator.multiply(BigInteger.TEN.pow(-scale));
            denominator = BigInteger.ONE;
        }

        return canonical(numerator, denominator, true);
    }

    private final BigInteger numerator;
    private final BigInteger denominator;

    /**
     * @param numerator   the numerator
     * @param denominator the denominator
     * @throws NullPointerException if numerator or denominator are null
     */
    private BigRational(BigInteger numerator, BigInteger denominator)
    {
        Preconditions.requireThat(numerator, "numerator").isNotNull();
        Preconditions.requireThat(denominator, "denominator").isNotNull();
        this.numerator = numerator;
        this.denominator = denominator;
    }

    /**
     * @return the numerator
     */
    public BigInteger getNumerator()
    {
        return numerator;
    }

    /**
     * @return the denominator
     */
    public BigInteger getDenominator()
    {
        return denominator;
    }

    @Override
    @SuppressWarnings("AccessingNonPublicFieldOfAnotherObject")
    public int compareTo(BigRational other)
    {
        Preconditions.requireThat(other, "other").isNotNull();

        // canonical() ensures denominator is positive
        if (numerator.signum() != other.numerator.signum())
            return numerator.signum() - other.numerator.signum();

        // Set the denominator to a common multiple before comparing the numerators
        BigInteger first = numerator.multiply(other.denominator);
        BigInteger second = other.numerator.multiply(denominator);
        return first.compareTo(second);
    }

    /**
     * @param other another rational fraction
     * @return the result of adding this object to {@code other}
     * @throws NullPointerException if other is null
     */
    @SuppressWarnings("AccessingNonPublicFieldOfAnotherObject")
    public BigRational add(BigRational other)
    {
        Preconditions.requireThat(other, "other").isNotNull();
        if (other.numerator.signum() == 0)
            return this;
        if (numerator.signum() == 0)
            return other;
        if (denominator.equals(other.denominator))
            return new BigRational(numerator.add(other.numerator), denominator);
        return canonical(numerator.multiply(other.denominator).
            add(other.numerator.multiply(denominator)),
            denominator.multiply(other.denominator), true);
    }

    /**
     * @param other another rational fraction
     * @return the result of subtracting {@code other} from this object
     * @throws NullPointerException if other is null
     */
    @SuppressWarnings("AccessingNonPublicFieldOfAnotherObject")
    public BigRational subtract(BigRational other)
    {
        return add(other.negate());
    }

    /**
     * @param other another rational fraction
     * @return the result of multiplying this object by {@code other}
     * @throws NullPointerException if other is null
     */
    @SuppressWarnings("AccessingNonPublicFieldOfAnotherObject")
    public BigRational multiply(BigRational other)
    {
        Preconditions.requireThat(other, "other").isNotNull();
        if (numerator.signum() == 0 || other.numerator.signum() == 0)
            return ZERO;
        if (numerator.equals(other.denominator))
            return canonical(other.numerator, denominator, true);
        if (other.numerator.equals(denominator))
            return canonical(numerator, other.denominator, true);
        if (numerator.negate().equals(other.denominator))
            return canonical(other.numerator.negate(), denominator, true);
        if (other.numerator.negate().equals(denominator))
            return canonical(numerator.negate(), other.denominator, true);
        return canonical(numerator.multiply(other.numerator), denominator.multiply(other.denominator),
            true);
    }

    /**
     * @param other another rational fraction
     * @return the result of dividing this object by {@code other}
     * @throws NullPointerException if other is null
     */
    public BigRational divide(BigRational other)
    {
        return multiply(other.invert());
    }

    /**
     * @return true if the object is a whole number
     */
    public boolean isInteger()
    {
        return numerator.signum() == 0 || denominator.equals(BigInteger.ONE);
    }

    /**
     * Returns a BigRational whose value is (-this).
     * <p>
     * @return -this
     */
    public BigRational negate()
    {
        return new BigRational(numerator.negate(), denominator);
    }

    /**
     * @return a rational fraction with the numerator and denominator swapped
     */
    public BigRational invert()
    {
        return canonical(denominator, numerator, false);
    }

    /**
     * @return the absolute value of this {@code BigRational}
     */
    public BigRational abs()
    {
        if (numerator.signum() < 0)
            return negate();
        return this;
    }

    /**
     * @param exponent exponent to which both numerator and denominator is to be raised.
     * @return a BigRational whose value is (this<sup>exponent</sup>).
     */
    public BigRational pow(int exponent)
    {
        return canonical(numerator.pow(exponent), denominator.pow(exponent), true);
    }

    /**
     * @param other another rational fraction
     * @return the minimum of this object and the other fraction
     */
    public BigRational min(BigRational other)
    {
        if (compareTo(other) <= 0)
            return this;
        return other;
    }

    /**
     * @param other another rational fraction
     * @return the maximum of this object and the other fraction
     */
    public BigRational max(BigRational other)
    {
        if (compareTo(other) >= 0)
            return this;
        return other;
    }

    /**
     * @param scale        scale of the BigDecimal quotient to be returned
     * @param roundingMode the rounding mode to apply
     * @return a BigDecimal representation of this object
     * @throws NullPointerException if roundingMode is null
     */
    public BigDecimal toBigDecimal(int scale, RoundingMode roundingMode)
    {
        Preconditions.requireThat(roundingMode, "roundingMode").isNotNull();
        if (isInteger())
            return new BigDecimal(numerator);
        return new BigDecimal(numerator).divide(new BigDecimal(denominator), scale, roundingMode);
    }

    @Override
    public int intValue()
    {
        return (int) longValue();
    }

    @Override
    public long longValue()
    {
        if (isInteger())
            return numerator.longValue();
        return numerator.divide(denominator).longValue();
    }

    @Override
    public float floatValue()
    {
        return (float) doubleValue();
    }

    @Override
    public double doubleValue()
    {
        if (isInteger())
            return numerator.doubleValue();
        return numerator.doubleValue() / denominator.doubleValue();
    }

    @Override
    @SuppressWarnings("AccessingNonPublicFieldOfAnotherObject")
    public boolean equals(Object o)
    {
        if (this == o)
            return true;
        if (!(o instanceof BigRational))
            return false;
        BigRational other = (BigRational) o;

        return numerator.equals(other.denominator) && Objects.equals(denominator, other.denominator);
    }

    @Override
    public int hashCode()
    {
        return Objects.hash(numerator, denominator);
    }

    /**
     * Returns the String representation: {@code numerator / denominator}.
     */
    @Override
    public String toString()
    {
        if (isInteger())
            return String.format("%,d", numerator);
        return String.format("%,d / %,d", numerator, denominator);
    }
}

Answer 11

I''ll third or fifth or whatever the recommendation for making your fraction immutable. I''d also recommend that you have it extend the Number class. I''d probably look at the Double class, since you''re probably going to want to implement many of the same methods.

You should probably also implement Comparable<T> and Serializable since this behavior will probably be expected. Thus, you will need to implement compareTo(). You will also need to override equals() and I cannot stress strongly enough that you also override hashCode(). This might be one of the few cases though where you don''t want compareTo() and equals() to be consistent since fractions reducable to each other are not necessarily equal.

Answer 12

If you multiply the numerator and denominator of one Fraction with the denominator of the other and vice versa, you end up with two fractions (that are still the same values) with the same denominator and you can compare the numerators directly. Therefore you wouldn''t need to calculate the double value:

public int compareTo(Fraction frac) {
    int t = this.numerator * frac.getDenominator();
    int f = frac.getNumerator() * this.denominator;
    if(t>f) return 1;
    if(f>t) return -1;
    return 0;
}

Answer 13

If you''re feeling adventurous, take a look at JScience . It has a Rational class that represents fractions.

Answer 14

Initial remark:

Never write this:

if ( condition ) statement;

This is much better

if ( condition ) { statement };

Just create to create a good habit.

By making the class immutable as suggested, you can also take advantage of the double to perform the equals and hashCode and compareTo operations

Here''s my quick dirty version:

public final class Fraction implements Comparable {

    private final int numerator;
    private final int denominator;
    private final Double internal;

    public static Fraction createFraction( int numerator, int denominator ) { 
        return new Fraction( numerator, denominator );
    }

    private Fraction(int numerator, int denominator) {
        this.numerator   = numerator;
        this.denominator = denominator;
        this.internal = ((double) numerator)/((double) denominator);
    }


    public int getNumerator() {
        return this.numerator;
    }

    public int getDenominator() {
        return this.denominator;
    }


    private double doubleValue() {
        return internal;
    }

    public int compareTo( Object o ) {
        if ( o instanceof Fraction ) { 
            return internal.compareTo( ((Fraction)o).internal );
        }
        return 1;
    }

    public boolean equals( Object o ) {
          if ( o instanceof Fraction ) {  
             return this.internal.equals( ((Fraction)o).internal );
          } 
          return false;
    }

    public int hashCode() { 
        return internal.hashCode();
    }



    public String toString() { 
        return String.format("%d/%d", numerator, denominator );
    }

    public static void main( String [] args ) { 
        System.out.println( Fraction.createFraction( 1 , 2 ) ) ;
        System.out.println( Fraction.createFraction( 1 , 2 ).hashCode() ) ;
        System.out.println( Fraction.createFraction( 1 , 2 ).compareTo( Fraction.createFraction(2,4) ) ) ;
        System.out.println( Fraction.createFraction( 1 , 2 ).equals( Fraction.createFraction(4,8) ) ) ;
        System.out.println( Fraction.createFraction( 3 , 9 ).equals( Fraction.createFraction(1,3) ) ) ;
    }       

}

About the static factory method, it may be useful later, if you subclass the Fraction to handle more complex things, or if you decide to use a pool for the most frequently used objects.

It may not be the case, I just wanted to point it out. :)

See Effective Java first item.

Answer 15

Might be useful to add simple things like reciprocate, get remainder and get whole.

Answer 16

Once you''ve created a fraction object why would you want to allow other objects to set the numerator or the denominator? I would think these should be read only. It makes the object immutable...

Also...setting the denominator to zero should throw an invalid argument exception (I don''t know what it is in Java)

Answer 17

One very minor improvement could potentially be to save the double value that you''re computing so that you only compute it on the first access. This won''t be a big win unless you''re accessing this number a lot, but it''s not overly difficult to do, either.

One additional point might be the error checking you do in the denominator...you automatically change 0 to 1. Not sure if this is correct for your particular application, but in general if someone is trying to divide by 0, something is very wrong. I''d let this throw an exception (a specialized exception if you feel it''s needed) rather than change the value in a seemingly arbitrary way that isn''t known to the user.

In constrast with some other comments, about adding methods to add subtract, etc...since you didn''t mention needing them, I''m assuming you don''t. And unless you''re building a library that is really going to be used in many places or by other people, go with YAGNI (you ain''t going to need it, so it shouldn''t be there.)

Answer 18

There are several ways to improve this or any value type:

• Make your class immutable , including making numerator and denominator final
• Automatically convert fractions to a canonical form , eg 2/4 -> 1/2
• Implement toString()
• Implement "public static Fraction valueOf(String s)" to convert from strings to fractions. Implement similar factory methods for converting from int, double, etc.
• Implement addition, multiplication, etc
• Add constructor from whole numbers
• Override equals/hashCode
• Consider making Fraction an interface with an implementation that switches to BigInteger as necessary
• Consider sub-classing Number
• Consider including named constants for common values like 0 and 1
• Consider making it serializable
• Test for division by zero
• Document your API

Basically, take a look at the API for other value classes like Double , Integer and do what they do :)

Answer 19

This function simplify using the eucledian algorithm is quite useful when defining fractions

 public Fraction simplify(){


     int safe;
     int h= Math.max(numerator, denominator);
     int h2 = Math.min(denominator, numerator);

     if (h == 0){

         return new Fraction(1,1);
     }

     while (h>h2 && h2>0){

          h = h - h2;
          if (h>h2){

              safe = h;
              h = h2;
              h2 = safe;

          }  

     }

  return new Fraction(numerator/h,denominator/h);

 }

Answer 20

Timothy Budd has a fine implementation of a Rational class in his "Data Structures in C++". Different language, of course, but it ports over to Java very nicely.

I''d recommend more constructors. A default constructor would have numerator 0, denominator 1. A single arg constructor would assume a denominator of 1. Think how your users might use this class.

No check for zero denominator? Programming by contract would have you add it.

Answer 21

Use Rational class from JScience library. It''s the best thing for fractional arithmetic I seen in Java.

Answer 22

You have a compareTo function already ... I would implement the Comparable interface.

May not really matter for whatever you''re going to do with it though.

Answer 23

how I would improve that code:

1. a constructor based on String Fraction(String s) //expect "number/number"
2. a copy constructor Fraction(Fraction copy)
3. override the clone method
4. implements the equals, toString and hashcode methods
5. implements the interface java.io.Serializable, Comparable
6. a method "double getDoubleValue()"
7. a method add/divide/etc...
8. I would make that class as immutable (no setters)

Answer 24

• Hazlo immutable ;
• Conviértalo en canonical , lo que significa que 6/4 se convierte en 3/2 (el mayor algoritmo de divisor común es útil para esto);
• Llámalo Racional, ya que lo que estás representando es un número racional ;
• Puede usar BigInteger para almacenar valores arbitrariamente precisos. Si no es así, entonces long , que tiene una implementación más fácil;
• Haz el denominador siempre positivo. El signo debe ser llevado por el numerador;
• Ampliar Number ;
• Implementar Comparable<T> ;
• Implementar equals() y hashCode() ;
• Agregue el método de fábrica para un número representado por una String ;
• Agregue algunos métodos de fábrica de conveniencia;
• Agregar un toString() ; y
• Hazlo Serializable .

De hecho, prueba esto para el tamaño. Se ejecuta pero puede tener algunos problemas:

public class BigRational extends Number implements Comparable<BigRational>, Serializable {
    public final static BigRational ZERO = new BigRational(BigInteger.ZERO, BigInteger.ONE);
    private final static long serialVersionUID = 1099377265582986378L;

    private final BigInteger numerator, denominator;

    private BigRational(BigInteger numerator, BigInteger denominator) {
        this.numerator = numerator;
        this.denominator = denominator;
    }

    private static BigRational canonical(BigInteger numerator, BigInteger denominator, boolean checkGcd) {
        if (denominator.signum() == 0) {
            throw new IllegalArgumentException("denominator is zero");
        }
        if (numerator.signum() == 0) {
            return ZERO;
        }
        if (denominator.signum() < 0) {
            numerator = numerator.negate();
            denominator = denominator.negate();
        }
        if (checkGcd) {
            BigInteger gcd = numerator.gcd(denominator);
            if (!gcd.equals(BigInteger.ONE)) {
                numerator = numerator.divide(gcd);
                denominator = denominator.divide(gcd);
            }
        }
        return new BigRational(numerator, denominator);
    }

    public static BigRational getInstance(BigInteger numerator, BigInteger denominator) {
        return canonical(numerator, denominator, true);
    }

    public static BigRational getInstance(long numerator, long denominator) {
        return canonical(new BigInteger("" + numerator), new BigInteger("" + denominator), true);
    }

    public static BigRational getInstance(String numerator, String denominator) {
        return canonical(new BigInteger(numerator), new BigInteger(denominator), true);
    }

    public static BigRational valueOf(String s) {
        Pattern p = Pattern.compile("(-?//d+)(?:.(//d+)?)?0*(?:e(-?//d+))?");
        Matcher m = p.matcher(s);
        if (!m.matches()) {
            throw new IllegalArgumentException("Unknown format ''" + s + "''");
        }

        // this translates 23.123e5 to 25,123 / 1000 * 10^5 = 2,512,300 / 1 (GCD)
        String whole = m.group(1);
        String decimal = m.group(2);
        String exponent = m.group(3);
        String n = whole;

        // 23.123 => 23123
        if (decimal != null) {
            n += decimal;
        }
        BigInteger numerator = new BigInteger(n);

        // exponent is an int because BigInteger.pow() takes an int argument
        // it gets more difficult if exponent needs to be outside {-2 billion,2 billion}
        int exp = exponent == null ? 0 : Integer.valueOf(exponent);
        int decimalPlaces = decimal == null ? 0 : decimal.length();
        exp -= decimalPlaces;
        BigInteger denominator;
        if (exp < 0) {
            denominator = BigInteger.TEN.pow(-exp);
        } else {
            numerator = numerator.multiply(BigInteger.TEN.pow(exp));
            denominator = BigInteger.ONE;
        }

        // done
        return canonical(numerator, denominator, true);
    }

    // Comparable
    public int compareTo(BigRational o) {
        // note: this is a bit of cheat, relying on BigInteger.compareTo() returning
        // -1, 0 or 1.  For the more general contract of compareTo(), you''d need to do
        // more checking
        if (numerator.signum() != o.numerator.signum()) {
            return numerator.signum() - o.numerator.signum();
        } else {
            // oddly BigInteger has gcd() but no lcm()
            BigInteger i1 = numerator.multiply(o.denominator);
            BigInteger i2 = o.numerator.multiply(denominator);
            return i1.compareTo(i2); // expensive!
        }
    }

    public BigRational add(BigRational o) {
        if (o.numerator.signum() == 0) {
            return this;
        } else if (numerator.signum() == 0) {
            return o;
        } else if (denominator.equals(o.denominator)) {
            return new BigRational(numerator.add(o.numerator), denominator);
        } else {
            return canonical(numerator.multiply(o.denominator).add(o.numerator.multiply(denominator)), denominator.multiply(o.denominator), true);
        }
    }


    public BigRational multiply(BigRational o) {
        if (numerator.signum() == 0 || o.numerator.signum( )== 0) {
            return ZERO;
        } else if (numerator.equals(o.denominator)) {
            return canonical(o.numerator, denominator, true);
        } else if (o.numerator.equals(denominator)) {
            return canonical(numerator, o.denominator, true);
        } else if (numerator.negate().equals(o.denominator)) {
            return canonical(o.numerator.negate(), denominator, true);
        } else if (o.numerator.negate().equals(denominator)) {
            return canonical(numerator.negate(), o.denominator, true);
        } else {
            return canonical(numerator.multiply(o.numerator), denominator.multiply(o.denominator), true);
        }
    }

    public BigInteger getNumerator() { return numerator; }
    public BigInteger getDenominator() { return denominator; }
    public boolean isInteger() { return numerator.signum() == 0 || denominator.equals(BigInteger.ONE); }
    public BigRational negate() { return new BigRational(numerator.negate(), denominator); }
    public BigRational invert() { return canonical(denominator, numerator, false); }
    public BigRational abs() { return numerator.signum() < 0 ? negate() : this; }
    public BigRational pow(int exp) { return canonical(numerator.pow(exp), denominator.pow(exp), true); }
    public BigRational subtract(BigRational o) { return add(o.negate()); }
    public BigRational divide(BigRational o) { return multiply(o.invert()); }
    public BigRational min(BigRational o) { return compareTo(o) <= 0 ? this : o; }
    public BigRational max(BigRational o) { return compareTo(o) >= 0 ? this : o; }

    public BigDecimal toBigDecimal(int scale, RoundingMode roundingMode) {
        return isInteger() ? new BigDecimal(numerator) : new BigDecimal(numerator).divide(new BigDecimal(denominator), scale, roundingMode);
    }

    // Number
    public int intValue() { return isInteger() ? numerator.intValue() : numerator.divide(denominator).intValue(); }
    public long longValue() { return isInteger() ? numerator.longValue() : numerator.divide(denominator).longValue(); }
    public float floatValue() { return (float)doubleValue(); }
    public double doubleValue() { return isInteger() ? numerator.doubleValue() : numerator.doubleValue() / denominator.doubleValue(); }

    @Override
    public String toString() { return isInteger() ? String.format("%,d", numerator) : String.format("%,d / %,d", numerator, denominator); }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        BigRational that = (BigRational) o;

        if (denominator != null ? !denominator.equals(that.denominator) : that.denominator != null) return false;
        if (numerator != null ? !numerator.equals(that.numerator) : that.numerator != null) return false;

        return true;
    }

    @Override
    public int hashCode() {
        int result = numerator != null ? numerator.hashCode() : 0;
        result = 31 * result + (denominator != null ? denominator.hashCode() : 0);
        return result;
    }

    public static void main(String args[]) {
        BigRational r1 = BigRational.valueOf("3.14e4");
        BigRational r2 = BigRational.getInstance(111, 7);
        dump("r1", r1);
        dump("r2", r2);
        dump("r1 + r2", r1.add(r2));
        dump("r1 - r2", r1.subtract(r2));
        dump("r1 * r2", r1.multiply(r2));
        dump("r1 / r2", r1.divide(r2));
        dump("r2 ^ 2", r2.pow(2));
    }

    public static void dump(String name, BigRational r) {
        System.out.printf("%s = %s%n", name, r);
        System.out.printf("%s.negate() = %s%n", name, r.negate());
        System.out.printf("%s.invert() = %s%n", name, r.invert());
        System.out.printf("%s.intValue() = %,d%n", name, r.intValue());
        System.out.printf("%s.longValue() = %,d%n", name, r.longValue());
        System.out.printf("%s.floatValue() = %,f%n", name, r.floatValue());
        System.out.printf("%s.doubleValue() = %,f%n", name, r.doubleValue());
        System.out.println();
    }
}

La salida es:

r1 = 31,400
r1.negate() = -31,400
r1.invert() = 1 / 31,400
r1.intValue() = 31,400
r1.longValue() = 31,400
r1.floatValue() = 31,400.000000
r1.doubleValue() = 31,400.000000

r2 = 111 / 7
r2.negate() = -111 / 7
r2.invert() = 7 / 111
r2.intValue() = 15
r2.longValue() = 15
r2.floatValue() = 15.857142
r2.doubleValue() = 15.857143

r1 + r2 = 219,911 / 7
r1 + r2.negate() = -219,911 / 7
r1 + r2.invert() = 7 / 219,911
r1 + r2.intValue() = 31,415
r1 + r2.longValue() = 31,415
r1 + r2.floatValue() = 31,415.857422
r1 + r2.doubleValue() = 31,415.857143

r1 - r2 = 219,689 / 7
r1 - r2.negate() = -219,689 / 7
r1 - r2.invert() = 7 / 219,689
r1 - r2.intValue() = 31,384
r1 - r2.longValue() = 31,384
r1 - r2.floatValue() = 31,384.142578
r1 - r2.doubleValue() = 31,384.142857

r1 * r2 = 3,485,400 / 7
r1 * r2.negate() = -3,485,400 / 7
r1 * r2.invert() = 7 / 3,485,400
r1 * r2.intValue() = 497,914
r1 * r2.longValue() = 497,914
r1 * r2.floatValue() = 497,914.281250
r1 * r2.doubleValue() = 497,914.285714

r1 / r2 = 219,800 / 111
r1 / r2.negate() = -219,800 / 111
r1 / r2.invert() = 111 / 219,800
r1 / r2.intValue() = 1,980
r1 / r2.longValue() = 1,980
r1 / r2.floatValue() = 1,980.180176
r1 / r2.doubleValue() = 1,980.180180

r2 ^ 2 = 12,321 / 49
r2 ^ 2.negate() = -12,321 / 49
r2 ^ 2.invert() = 49 / 12,321
r2 ^ 2.intValue() = 251
r2 ^ 2.longValue() = 251
r2 ^ 2.floatValue() = 251.448975
r2 ^ 2.doubleValue() = 251.448980

Answer 25

• It''s kinda pointless without arithmetic methods like add() and multiply(), etc.
• You should definitely override equals() and hashCode().
• You should either add a method to normalize the fraction, or do it automatically. Think about whether you want 1/2 and 2/4 to be considered the same or not - this has implications for the equals(), hashCode() and compareTo() methods.