如何覆盖 compareTo 方法？

Question

I want to override the compareTo method. I googled hard but couldn't find anything useful, because my K is not specifically defined (it is not like People(class example) with name, age).

I have file Node.java that I cannot edit.

public class Node<K extends Comparable<K>, V>
{
    public K key;
    public V value;

    public Node<K, V> parent;
    public Node<K, V> left;
    public Node<K, V> right;

    public Node(K key, V value, Node<K, V> parent, Node<K, V> left, Node<K, V> right)
    {
        this.key = key;
        this.value = value;

        this.parent = parent;
        this.left = left;
        this.right = right;
    }
}

and I have the other file Heap.java

public class Heap<K extends Comparable<K>, V> {...}

I want to override compareTo method at Heap.java (inside {..} here!) so I can compare Node's key and sort them.

Answer 1

Instead of overriding compareTo , you can create a Comparator<Node> like this:

Comparator<Node<K extends Comparable<K>>, V> comparator =
        Comparator.comparing(node -> node.key);

You can use it for sorting in most library methods, eg in the case of sorted maps, you can pass a Comparator.

Note however that it is a bad idea to have a public key field. It would be bad enough by itself, but if you use it for storing its even worse because you'll mess up the short when someone else changes the field.

Answer 2

If you want object to be used as a natural sorting key then you use comparable on that object, ie Heap implement Comparable will make you override it then you can use your heap object in node. And if you want your heap object to sort comparable object best way would be to look at the implementation in Collections class.

Answer 3

You can create the comparator as follows if you can provide compareTo inside classes corresponding to K

Comparator<Node<K, V>> comparator = new Comparator<Node<K, V>>() {
    @Override
    public int compare(Node<K, V> node1, Node<K, V> node2) {
        return node1.key.compareTo(node2.key);
    }
};

you can use this comparator anywhere, for example to sort list of nodes, you can simply do Collections.sort(nodes, comparator)

You can also bind K to an interface which gives you method to get value of key, and use it in Heap.java to define your complete logic there itself