LRU Cache LeetCode solution in Java

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class LRUCache {
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  // Declare Node class for Doubly Linked List
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  class Node {
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    int key, value; // to store key and value
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    Node next, prev; // Next and Previous Pointers
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    Node(int k, int v) {
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      key = k;
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      value = v;
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    }
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  }
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  Node head = new Node(-1, -1); // Default values
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  Node tail = new Node(-1, -1);
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  Map<Integer, Node> mp; // to store key and Node
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  int cap;
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  public LRUCache(int capacity) {
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    // initializing in constructor
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    cap = capacity;
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    head.next = tail;
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    tail.prev = head;
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    mp = new HashMap<Integer, Node>();
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  }
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  public int get(int key) {
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    // if map contains the specific key
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    if (mp.containsKey(key)) {
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      Node existing = mp.get(key);
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      del(existing);
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      ins(existing); // reinserting to keep key after the head pointer and to update LRU list
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      return existing.value;
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    }
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    // otherwise
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    return -1;
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  }
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  public void put(int key, int value) {
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    // if map contains the key
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    if (mp.containsKey(key)) {
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      Node existing = mp.get(key);
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      // remove from the map and delete from the LRU list
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      mp.remove(key);
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      del(existing);
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    }
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    // if map size is equal to spcified capacity of the LRU list
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    if (mp.size() == cap) {
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      // remove from the map and delete from the LRU list
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      mp.remove(tail.prev.key);
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      del(tail.prev);
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    }
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    Node newNode = new Node(key, value);
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    ins(newNode);
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    mp.put(key, head.next);
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  }
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  public void ins(Node newNode) {
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    // Insert always after the head of the linkedList
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    Node temp = head.next;
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    head.next = newNode;
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    newNode.prev = head;
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    newNode.next = temp;
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    temp.prev = newNode;
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  }
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  public void del(Node newNode) {
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    // Remove the specified node using previous and next pointers
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    Node pr = newNode.prev;
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    Node nx = newNode.next;
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    pr.next = nx;
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    nx.prev = pr;
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  }
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}