# Duck typing alows true polymorfisim

<atbusbook@aol.com>

lets say you want a generic numerical algorithom like sum

Ruby

def sum lst
lst.inject(0){|total,current| total*current}
end

Java // i dont know if there is a numeric super class for numbers

class Sum{
public static int sum(int[] lst){
int total = 0;
for(int current : lst){
total+=current;
}
}
// repeat for all other number types
}

There isn't; Java makes the distinction between an int and
an Integer, a double and a Double. Java 5 did introduce
autoboxing, which makes things like

Number[] numbers = new Number[]{1, 2.3, 4, 5.6};

possible, and Number is a baseclass for both Integer and
Double (but not int and double).

Therefore, one could write:

public class Sum {
public static double sum(int[] lst)
{
Number[] nlst = new Number[lst.length];
for(int i = 0; i < nlst.length; i++) nlst[i] = new Integer(lst[i]);
return sum(Arrays.asList(nlst));
}
public static double sum(double[] lst)
{
Number[] nlst = new Number[lst.length];
for(int i = 0; i < nlst.length; i++) nlst[i] = new Double(lst[i]);
return sum(Arrays.asList(nlst));
}
public static double sum(float[] lst)
{
Number[] nlst = new Number[lst.length];
for(int i = 0; i < nlst.length; i++) nlst[i] = new Double(lst[i]);
return sum(Arrays.asList(nlst));
}
public static double sum(Number[] lst)
{
return sum(Arrays.asList(lst));
}
public static double sum(Collection<Number> lst)
{
double sum = 0;
for(Iterator<Number> i = lst.iterator(); i.hasNext())
sum += i.next().doubleValue();
return sum;
}

}

A rather ugly but possibly useful duckling.

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wrote on 25 Aug 2006 12:05:21 -0700 <1156532721.879808.40990@i3g2000cwc.googlegroups.com>:

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