import java.util.ArrayList;

class Pair<T> {
    private T first;
    private T second;

    public Pair() {
    }

    public Pair(T x1, T x2) {
        first = x1;
        second = x2;
    }

}

public class Main {

    public static <E> void append(ArrayList<E> list) {
        // E elem = new E(); // compile-time error: Cannot instantiate the type E
        // list.add(elem);
    }

    public static <E> void append(ArrayList<E> list, E elem) // OK
    {
        list.add(elem);
    }

    public static void main(String[] args) {
        String[] x1 = new String[3]; // OK

        // Error: Cannot create a generic array of Pair<String>
        // Pair<String>[] x2 = new Pair<String>[3];

        Pair<Integer> li = new Pair<>();

        // Type mismatch: cannot convert from Pair<Integer> to Pair<Number>
        // Pair<Number> ln = li;

        Pair<? extends Number> ln = li; // OK
    }

}