1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/task2/solution04/src/org/apidesign/apifest08/currency/ConvertorFactory.java	Wed Oct 01 10:43:05 2008 +0200
     1.3 @@ -0,0 +1,116 @@
     1.4 +package org.apidesign.apifest08.currency;
     1.5 +
     1.6 +import java.lang.ref.WeakReference;
     1.7 +import java.math.BigDecimal;
     1.8 +import java.util.Currency;
     1.9 +import java.util.Map;
    1.10 +import java.util.WeakHashMap;
    1.11 +
    1.12 +
    1.13 +/**
    1.14 + * Create convertors using a flyweight to reduce the number of repetative creations of the same convertor.
    1.15 + * 
    1.16 + * @author D'Arcy Smith
    1.17 + * @version 1.0
    1.18 + */
    1.19 +public final class ConvertorFactory
    1.20 +{
    1.21 +    /**
    1.22 +     * flyweight so that only one vestion of each converter is created at a time.
    1.23 +     */
    1.24 +    private final static Map<String, WeakReference<Convertor>> convertors;
    1.25 +    
    1.26 +    static
    1.27 +    {
    1.28 +        convertors = new WeakHashMap<String, WeakReference<Convertor>>();
    1.29 +    }
    1.30 +    
    1.31 +    /** 
    1.32 +     * Prevent accidental construction.
    1.33 +     */
    1.34 +    private ConvertorFactory()
    1.35 +    {        
    1.36 +    }
    1.37 +    
    1.38 +    /**
    1.39 +     * Get the convertor for the specified currencies.  The currency name format
    1.40 +     * must be acceptable to java.util.Currency.getInstance(String)
    1.41 +     * 
    1.42 +     * @param a the currency to convert from.
    1.43 +     * @param aRate the exchange rate for a to b.
    1.44 +     * @param b the currency to convert to.
    1.45 +     * @param bRate the echante rate for b to a.
    1.46 +     * @return the convertor for the specified currencies.
    1.47 +     * @throws IllegalArgumentException if any of the arguments are null.
    1.48 +     */
    1.49 +    public static Convertor getConvertor(final String     a,
    1.50 +                                         final BigDecimal aRate,
    1.51 +                                         final String     b,
    1.52 +                                         final BigDecimal bRate)
    1.53 +    {
    1.54 +        final Currency  currencyA;
    1.55 +        final Currency  currencyB;
    1.56 +        final Convertor convertor;
    1.57 +        
    1.58 +        currencyA = Currency.getInstance(a);
    1.59 +        currencyB = Currency.getInstance(b);        
    1.60 +        convertor = getConvertor(currencyA, aRate, currencyB, bRate);
    1.61 +        
    1.62 +        return (convertor);
    1.63 +    }
    1.64 +    
    1.65 +    /**
    1.66 +     * Get the convertor for the specified currencies.
    1.67 +     * 
    1.68 +     * @param a the currency to convert from.
    1.69 +     * @param aRate the exchange rate for a to b.
    1.70 +     * @param b the currency to convert to.
    1.71 +     * @param bRate the echante rate for b to a.
    1.72 +     * @return the convertor for the specified currencies.
    1.73 +     * @throws IllegalArgumentException if either any of the arguments are null or if either rate <= 0.
    1.74 +     */
    1.75 +    public static Convertor getConvertor(final Currency   a,
    1.76 +                                         final BigDecimal aRate,
    1.77 +                                         final Currency   b,
    1.78 +                                         final BigDecimal bRate)
    1.79 +    {
    1.80 +        final String key;        
    1.81 +        Convertor    convertor;
    1.82 +
    1.83 +        if(a == null)
    1.84 +        {
    1.85 +            throw new IllegalArgumentException("a cannot be null");
    1.86 +        }
    1.87 +
    1.88 +        if(b == null)
    1.89 +        {
    1.90 +            throw new IllegalArgumentException("b cannot be null");
    1.91 +        }
    1.92 +        
    1.93 +        if(aRate == null)
    1.94 +        {
    1.95 +            throw new IllegalArgumentException("aRate cannot be null");
    1.96 +        }
    1.97 +        
    1.98 +        if(bRate == null)
    1.99 +        {
   1.100 +            throw new IllegalArgumentException("bRate cannot be null");
   1.101 +        }
   1.102 +
   1.103 +        key = a.getCurrencyCode() + aRate + b.getCurrencyCode() + bRate;
   1.104 +
   1.105 +        // make sure that we don't try to overwrite one
   1.106 +        synchronized(convertors)
   1.107 +        {
   1.108 +            if(!(convertors.containsKey(key)))
   1.109 +            {        
   1.110 +                convertor = new ConvertorImpl(a, aRate, b, bRate);
   1.111 +                convertors.put(key, new WeakReference(convertor));
   1.112 +            }
   1.113 +        }
   1.114 +
   1.115 +        convertor = convertors.get(key).get();
   1.116 +        
   1.117 +        return (convertor);
   1.118 +    }
   1.119 +}