private Node head;
private Node end;
//缓存存储上限
private int limit;
private HashMap<String, Node> hashMap;
public LRUCache(int limit) {
this.limit = limit;
hashMap = new HashMap<String, Node>();
}
public String get(String key) {
Node node = hashMap.get(key);
if (node == null){
return null;
}
refreshNode(node);
return node.value;
}
public void put(String key, String value) {
Node node = hashMap.get(key);
if (node == null) {
//如果key不存在，插入key-value
if (hashMap.size() >= limit) {
String oldKey = removeNode(head);
hashMap.remove(oldKey);
}
node = new Node(key, value);
addNode(node);
hashMap.put(key, node);
}else {
//如果key存在，刷新key-value
node.value = value;
refreshNode(node);
}
}
public void remove(String key) {
Node node = hashMap.get(key);
removeNode(node);
hashMap.remove(key);
}
/**
* 刷新被访问的节点位置
* @param node 被访问的节点
*/
private void refreshNode(Node node) {
//如果访问的是尾节点，无需移动节点
if (node == end) {
return;
}
//移除节点
removeNode(node);
//重新插入节点
addNode(node);
}
/**
* 删除节点
* @param node 要删除的节点
*/
private String removeNode(Node node) {
if (node == end) {
//移除尾节点
end = end.pre;
}else if(node == head){
//移除头节点
head = head.next;
} else {
//移除中间节点
node.pre.next = node.next;
node.next.pre = node.pre;
}
return node.key;
}
/**
* 尾部插入节点
* @param node 要插入的节点
*/
private void addNode(Node node) {
if(end != null) {
end.next = node;
node.pre = end;
node.next = null;
}
end = node;
if(head == null){
head = node;
}
}
class Node {
Node(String key, String value){
this.key = key;
this.value = value;
}
public Node pre;
public Node next;
public String key;
public String value;
}
public static void main(String[] args) {
LRUCache lruCache = new LRUCache(5);
lruCache.put("001", "用户1信息");
lruCache.put("002", "用户1信息");
lruCache.put("003", "用户1信息");
lruCache.put("004", "用户1信息");
lruCache.put("005", "用户1信息");
lruCache.get("002");
lruCache.put("004", "用户2信息更新");
lruCache.put("006", "用户6信息");
System.out.println(lruCache.get("001"));
System.out.println(lruCache.get("006"));
}
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