캐 시 란 무엇 입 니까?

    //   
  public class LinkedList {
  
      public LinkedList() {
          size = 0;
      }
  
      Node list;
      //        
      int size;
  
      //    
      //       
      public void add(T data) {
          Node head = list;
          Node curNode = new Node(data, list);
          list = curNode;
          size++;
  
      }
  
      //    index         
      public void add(int index, T data) {
          checkPositionIndex(index);
          Node cur = list;
          Node hrad = list;
          for (int i = 0; i < index; i++) {
              hrad = cur;
              cur = cur.next;
          }
          Node node = new Node(data, cur);
          hrad.next = node;
          size++;
  
      }
  
      //   index          
      public void checkPositionIndex(int index) {
          if (!(index >= 0 && index <= size)) {
              throw new IndexOutOfBoundsException("index:" + index + ",size" + size);
          }
      }
  
      //    
      public T remove() {
          if (list != null) {
              Node node = list;
              list = list.next;
              //gc
              node.next = null;
              size--;
              return node.data;
          }
  
          return null;
      }
  
      public T remove(int index) {
          checkPositionIndex(index);
          Node cur = list;
          Node hrad = list;
          for (int i = 0; i < index; i++) {
              hrad = cur;
              cur = cur.next;
          }
          hrad.next = cur.next;
          //gc
          cur.next = null;
          size--;
          return null;
  
      }
  
      public T removeLast() {
          if (list != null) {
              Node node = list;
              Node cur = list;
              while (cur.next != null) {
                  node = cur;
                  cur = cur.next;
              }
              //gc
              node.next = null;
              size--;
              return cur.data;
          }
          return null;
      }
  
      //    
  
      public void updata(int index, T newData) {
          checkPositionIndex(index);
          Node head = list;
          for (int i = 0; i < index; i++) {
              head = head.next;
          }
          head.data = newData;
      }
  
      //    
      public T get() {
          Node node = list;
          if (node != null) {
              return node.data;
  
          } else {
              return null;
          }
      }
  
      public T get(int index) {
          checkPositionIndex(index);
          Node node = list;
          for (int i = 0; i < index; i++) {
              node = node.next;
          }
          return node.data;
      }
  
  
      class Node {
          T data;
          Node next;
  
          public Node(T data,
                      Node next) {
              this.data = data;
              this.next = next;
          }
      }
  
      @Override
      public String toString() {
          Node node = list;
          for (int i = 0; i < size; i++) {
              System.out.println("" + node.data);
  
              node = node.next;
          }
          return super.toString();
      }
  }

public class LruLinhedList extends LinkedList {

    //            
    int memorySize;
    static final int DEFAULT_CAP = 6;

    public LruLinhedList() {
        this(DEFAULT_CAP);
    }

    public LruLinhedList(int memorySize) {
        this.memorySize = memorySize;
    }

    //    LRU     
    public void lruAdd(T data) {
        if (size >= memorySize) {
            removeLast();
            add(data);
        } else {
            add(data);
        }
    }

    //     
    public T lruRmove() {
        return removeLast();
    }

    public T lruGet(int index) {
        checkPositionIndex(index);
        Node node = list;
        Node pro = list;
        for (int i = 0; i < index; i++) {
            pro = node;
            node = node.next;
        }
        T reData = node.data;
        //       
        pro.next = node.next;
        Node head = list;
        node.next = head;
        list = node;
        return reData;

    }

    public static void main(String[] args) {
        LruLinhedList LinkedList = new LruLinhedList<>(6);
        for (int i = 0; i < 6; i++) {
            LinkedList.lruAdd("" + i);
        }
        LinkedList.toString();
        System.out.println("" + LinkedList.lruGet(4));

        LinkedList.toString();
        LinkedList.lruAdd(90+"");
        LinkedList.toString();
//        LinkedList.lruGet(23);
//        LinkedList.toString();
    }

}