What does the following Java code output?

public class GenericExample<T extends Number> {
    private T number;
    public GenericExample(T number) {
        this.number = number;
    }
    public double square() {
        return number.doubleValue() * number.doubleValue();
    }
    public static void main(String[] args) {
        GenericExample<Integer> example = new GenericExample<>(3);
        System.out.println(example.square());
    }
}