难以理解"泛型"的例子

public class GenericList<T> {
    private T[] elements;
    private int size;

    public GenericList(int capacity) {
        elements = (T[]) new Object[capacity];
        size = 0;
    }

    public void add(T element) {
        elements[size] = element;
        size++;
    }

    public T get(int index) {
        return elements[index];
    }

    public int size() {
        return size;
    }
}

GenericList<Integer> integerList = new GenericList<>(10);
integerList.add(1);
integerList.add(2);
integerList.add(3);

int firstElement = integerList.get(0);
int listSize = integerList.size();