我们可以用Java中的泛型做些什么来使它们看起来更好:

public class Pair<T, U> {
    private T key;
    private U value;

    public Pair(T key, U value) {
        this.key = key;
        this.value = value;
    }

    public T getKey() {
        return key;
    }

    public U getValue() {
        return value;
    }
}

public static <T> void swap(T[] arr, int i, int j) {
    T temp = arr[i];
    arr[i] = arr[j];
    arr[j] = temp;
}

public interface Converter<T, U> {
    U convert(T obj);
}

public class MyList<T extends Number> {
    private List<T> list;

    public MyList() {
        list = new ArrayList<>();
    }

    public void add(T item) {
        list.add(item);
    }

    public List<T> getList() {
        return list;
    }
}

public void addAll(List<? extends Number> list) {
    for (Number number : list) {
        this.list.add(number);
    }
}