Adding generic type objects

Question

I have an array list of generic types and i'm trying to create a method to calculate the average, but I cannot add the a generic without casting it first but I'm suppose to pass in integers or double how can i do this?

private ArrayList<T> grades;

public double computeAverage()
{
    double average = 0;
    double sum = 0;

    for (int i = 0; i < grades.size(); i++) {
        sum = sum + grades.get(i);  <<< ERROR
    }

    average = sum/grades.size();

    return average;

}

Error: The operator + is undefined for the argument type(s) double, T

Okay, I'm glad you showed us your error. Now, is T declared at the class level? How do you instantiate the instance of this object? — Makoto
– Makoto, Commented Feb 23, 2014 at 18:29
@Makoto I guess that information doesn't really matter here. Clearly we can't use + operator with type T. — Rohit Jain
– Rohit Jain, Commented Feb 23, 2014 at 18:31

qqilihq · Accepted Answer · 2014-02-23 18:31:28Z

8

Still, after your edit, its unclear what T is. If you're able to narrow it down to a Number (which is the super class for Integer and Double as you mentioned), the following will work:

List<Number> numbers = new ArrayList<Number>();

for (Number number : numbers) {
    sum += number.doubleValue();
}

edited Feb 23, 2014 at 18:31

answered Feb 23, 2014 at 18:25

qqilihq

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