二分搜索树Map

public class BSTMap
     
      ,V> implements Map
      
        {    private class Node    {        public K key;        public V value;        public Node left,right;        public Node(K key,V value)        {            this.key = key;            this.value = value;            left = null;            right = null;        }    }    private Node root;    private int size;    public BSTMap()    {        root = null;        size = 0;    }    @Override    public void add(K key, V value) {        root = add(root,key,value);    }    private Node add(Node node,K key,V value)    {        if (node == null)        {            size ++;            return new Node(key,value);        }        if (key.compareTo(node.key) < 0)        {            node.left = add(node.left,key,value);        }else if(key.compareTo(node.key) > 0)        {            node.right = add(node.right,key,value);        }else {            node.value = value;        }        return node;    }    @Override    public V remove(K key) {        Node node = getNode(root,key);        if (node != null){            root = remove(root,key);            return node.value;        }        return null;    }    private Node remove(Node node,K key)    {        if (node == null)        {            return null;        }        if (key.compareTo(node.key) < 0)        {            node.left = remove(node.left,key);            return node;        }else if(key.compareTo(node.key) > 0)        {            node.right = remove(node.right,key);            return node;        }else {            if (node.left == null)            {                Node rightNode = node.right;                node.right = null;                size--;                return rightNode;            }            if (node.right == null)            {                Node leftNode = node.left;                node.left = null;                size--;                return leftNode;            }            Node successor = minimum(node.right);            successor.right = removeMin(node.right);            node.left = node.right = null;            return successor;        }    }    private Node getNode(Node node,K key)    {        if (node == null)        {            return null;        }        if (key.compareTo(node.key) == 0)        {            return node;        }else if (key.compareTo(node.key) < 0)        {            return getNode(node.left,key);        }else {            return getNode(node.right,key);        }    }    @Override    public boolean contains(K key) {        return getNode(root,key) != null;    }    @Override    public V get(K key) {        Node node = getNode(root,key);        return node == null ? null : node.value;    }    @Override    public void set(K key, V newValue) {        Node node = getNode(root,key);        if (node == null)        {            throw new IllegalArgumentException( key + " is not exist");        }        node.value = newValue;    }    @Override    public int getSize() {        return size;    }    @Override    public boolean isEmpty() {        return size == 0;    }    private Node minimum(Node node)    {        if (node.left == null)        {            return node;        }        return minimum(node.left);    }    private Node removeMin(Node node)    {        if (node.left == null)        {            Node rightNode = node.right;            node.right = null;            size --;            return rightNode;        }        node.left = removeMin(node.left);        return node;    }}