package bstmap;

import java.util.Iterator;
import java.util.Set;

public class BSTMap<K extends Comparable<K>, V> implements Map61B<K, V>{
    private static class Node <K, V>{
        private final K key;
        private final V value;
        private Node left;
        private Node right;

        private Node(K key, V value) {
            this.key = key;
            this.value = value;
            this.left = null;
            this.right = null;
        }
    }

    private Node root;
    private int size;

    public BSTMap() {
        root = null;
        size = 0;
    }

    @Override
    public boolean containsKey(K key) {
        Node current = root;
        while (current != null) {
            if (current.key.equals(key)) {
                return true;
            }
            if (current.key.compareTo(key) < 0) {
                current = current.right;
            } else {
                current = current.left;
            }
        }
        return false;
    }

There is an error at “current.key.compareTo(key)”.

I had already created a bounded type parameter at the class header BSTMap where K should extends Comparable but why there’s still an error at the line of invoking compareTo method on key of type K.
I found out that to resolve this error I must explicitly declare that K extends Comparable again at the header for inner class Node but I thought Java should be able that K extends Comparable automatically upon declaring it at the BSTMap header and this applies to all other methods I am creating. Thus, may I know when should I explicitly declare a bounded type parameter in a class other than specifying it at the class header?