Jakarta Commons Cookbook

8.1. Using Fractions

Problem

You need to work with fractions supplied by the user, such as 3 4/5 and 134/21. Your application needs to parse, multiply, and reduce fractions.

Solution

Use Jakarta Commons Lang’s Fraction class to parse and manipulate fractions. The following code demonstrates the parsing of a String containing a fraction:

import org.apache.commons.lang.math.Fraction;

String userInput = "23 31/37";
Fraction fraction = Fraction.getFraction( userInput );
double value = fraction.doubleValue( );

The String “23 31/37” is converted to a double value of 23.837837. A Fraction object is created by calling the Fraction.getFraction( ) method, and double value of the Fraction object is obtained with fraction.doubleValue( ).

Discussion

The Fraction class provides a number of operations that can be used to simplify the following expression to an improper fraction. The following code evaluates the expression in Figure 8-1 using Fraction:

import org.apache.commons.lang.math.Fraction;

Fraction numer1 = Fraction.getFraction( 3, 4 );
Fraction numer2 = Fraction.getFraction( 51, 3509 );

Fraction numerator = numer1.multiplyBy( numer2 );
Fraction denominator = Fraction.getFraction( 41, 59 );

Fraction fraction = numerator.divideBy( denominator );
Fraction result = fraction.reduce( );

System.out.println( "as Fraction: " + result.reduce( ).toString( ) );
System.out.println( "as double: " + result.doubleValue( ) );

Figure 8-1. Expression to be evaluated with Fraction

The previous example creates ...