How to get the average of a generic array list in java? - class

Question

i'm having trouble getting the average of a generic array list of type T.

Answer 1

You should use <T extends Number> generic signature to specify the type of the Number types, plus, you should use instanceof keyword. A simple dummy demo here;
Test Code
import java.util.ArrayList;
import java.util.List;
public class Test {
public static void main(String[] args) {
List<Integer> integerList = new ArrayList<Integer>();
List<Double> doubleList = new ArrayList<Double>();
List<Float> floatList = new ArrayList<Float>();
for(int i = 0; i < 10; i++)
{
integerList.add(new Integer(i+1));
doubleList.add(new Double(i+1));
floatList.add(new Float(i+1));
}
Utility<Integer> utilityInteger = new Utility<Integer>(integerList);
Utility<Double> utilityDouble = new Utility<Double>(doubleList);
Utility<Float> utilityFloat = new Utility<Float>(floatList);
System.out.println("Integer average: " + utilityInteger.getAverage());
System.out.println("Double average : " + utilityDouble.getAverage());
System.out.println("Float average : " + utilityFloat.getAverage());
}
public static class Utility<T extends Number>
{
// Fields
private List<T> list;
private Object average;
// Constructor
#SuppressWarnings("unchecked")
public Utility(List<T> list)
{
this.list = list;
T sample = list.get(0);
if(sample instanceof Double)
{
doAverageDouble((List<Double>) list);
}
else if (sample instanceof Integer)
{
doAverageInteger((List<Integer>) list);
}
else if (sample instanceof Float)
{
doAverageFloat((List<Float>) list);
}
else
{
throw new IllegalStateException("Constructor must be initialiez with either of Double, Integer or Float list");
}
}
// Methods
private void doAverageDouble(List<Double> list) {
Double sum = new Double(0);
for(Double d : list)
{
sum += d;
}
average = sum/new Double(list.size());
}
private void doAverageInteger(List<Integer> list) {
Integer sum = new Integer(0);
for(Integer d : list)
{
sum += d;
}
average = sum/new Integer(list.size());
}
private void doAverageFloat(List<Float> list) {
Float sum = new Float(0);
for(Float d : list)
{
sum += d;
}
average = sum/new Float(list.size());
}
Object getAverage()
{
return average;
}
}
}
Console Output
Integer average: 5
Double average : 5.5
Float average : 5.5