1class NumberBox<T extends Number> {
2    private T value;
3 
4    public NumberBox(T value) {
5        this.value = value;
6    }
7 
8    public double doubleValue() {
9        return value.doubleValue();
10    }
11}
12 
13public class Main {
14    public static void main(String[] args) {
15        NumberBox<Integer> intBox = new NumberBox<>(5);
16        NumberBox<Double> dblBox = new NumberBox<>(3.14);
17 
18        System.out.println(intBox.doubleValue());
19        System.out.println(dblBox.doubleValue());
20    }
21}