LRU算法的应用 - ToB企服应用市场:ToB评测及商务社交产业平台

public class LRUCache {
private Node head;
private Node end;
private int limit;
private HashMap<String, Node> hashMap;
public LRUCache(int limit) {
this.limit = limit;
hashMap = new HashMap<>();
}
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) {
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，则刷新key-value
node.value = value;
refreshNode(node);
}
}
public void remove(String key){
Node node = hashMap.get(key);
refreshNode(node);
hashMap.remove(key);
}
/**
* 刷新被访问节点的位置
*
* @param node 被访问节点
*/
private void refreshNode(Node node) {
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
* @return
*/
private String removeNode(Node node) {
if (node == head && node == end) {
//移除唯一节点
head = null;
end = null;
} else if (node == end) {
//移除尾结点
end = end.pre;
end.next = null;
} else if (node == head) {
//移除头节点
head = head.next;
head.pre = null;
} else {
//移除中间节点
node.pre.next = node.next;//将当前节点的下一个，赋值给上一节点的下一个
node.next.pre = node.pre;//将当前节点的前一个，赋值给上一节点的前一个
}
return node.key;
}
private void addNode(Node node) {
if (end != null) {
end.next = node;
node.pre = end;
node.next = null;
}
end = node;
if (head == null)
head = node;
}
private static 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2信息");
lruCache.put("003","用户3信息");
lruCache.put("004","用户4信息");
lruCache.put("005","用户5信息");
lruCache.get("002");
lruCache.put("004","new用户4信息");
lruCache.put("006","用户6信息");
System.out.println(lruCache.get("001"));
System.out.println(lruCache.get("006"));
}
}

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