Drill 17: Key term — Generics in depth

import java.util.List;

class Box<T> {
    private final T value;

    Box(T value) {
        this.value = value;
    }

    public T value() {
        return value;
    }
}

class Numbers {
    public static double sum(List<? extends Number> values) {
        double total = 0;
        for (Number value : values) {
            total += value.doubleValue();
        }
        return total;
    }

    public static <T extends Comparable<T>> T max(List<T> values) {
        T best = values.get(0);
        for (T value : values) {
            if (value.compareTo(best) > 0) {
                best = value;
            }
        }
        return best;
    }
}