Practice›Java Fundamentals›Module 9. Generics›9.3 Wildcards

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9.3 Wildcards — sum any list of numbers

Total: 0 / 3 pts

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Task

Fill in sumAll so that it returns the sum of the list as a double.

Thanks to ? extends Number the same method takes a List<Integer> and a List<Double> — without the wildcard it would accept neither. The program prints 6.0 and 4.0.

Your solution

import java.util.ArrayList;
import java.util.List;

public class Main {

    public static double sumAll(List<? extends Number> nums) {
        // read every element as a Number and add it up

    }

    public static void main(String[] args) {
        List<Integer> ints = new ArrayList<Integer>();
        ints.add(1);
        ints.add(2);
        ints.add(3);
        List<Double> dbls = new ArrayList<Double>();
        dbls.add(1.5);
        dbls.add(2.5);
        System.out.println(sumAll(ints));
        System.out.println(sumAll(dbls));
    }
}

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