实现可比较的泛型类

Question

I have been assigned the problem: Write a generic WeightedElement<E,W> class which stores an element of type E and a weight of type W. It should implement Comparable relying on W's compareTo(). You should enforce that W itself is comparable.

So far I have made the class and implemented comparable but am encountering issue when making the compareTo() method for W. I have:

public class WeightedElement<E, W extends Comparable<W>> {

    public E element;
    public W weight;


    public WeightedElement() {
        element = this.element;
        weight = this.weight;
    }

    public int compareTo(W data) {
        if (this.weight == data.weight) {
            return 0;
        } else if (this.weight < data.weight) {
            return 1;
        } else {
            return 1;
        }
    }
}

I am encountering the issue that when I compare the weights, the weight for data is not found. Also are there any other methods I have to create to properly have a class that implements comparable on one of the variables? Thank you for any help

Answer 1

您拥有正确的泛型，但就像WeightedElement本身一样，您必须对权重调用compareTo —— 不能使用<或==进行比较。

Answer 2

public class WeightedElement<E, W extends Comparable<W>> implements Comparable<WeightedElement<E, W>> {

    private final E element;
    private final W weight;

    public WeightedElement(E element, W weight) {
        this.element = element;
        this.weight = Objects.requireNonNull(weight, "'weight' should not be null");
    }

    @Override
    public int compareTo(WeightedElement<E, W> other) {
        return other == null ? 1 : weight.compareTo(other.weight);
    }
}