Android | LruCache cache strategy

Introduction to LruCache

LruCache is a cache class in Android that uses the Least Recently Used strategy to manage cached data. LruCache can be used to cache frequently used data to improve application performance.

The working principle of LruCache is implemented through a bidirectional linked list and a hash table. The bidirectional linked list is used to store cached data in the order of access. The most recently accessed data will be placed at the head of the linked list, and the data that has not been accessed for the longest time will be placed at the tail of the linked list. The hash table is used to quickly find cached data.

When data needs to be obtained from LruCache, LruCache will first search for the corresponding cache data in the hash table. If it is found, it will move the data to the head of the linked list and return it to the caller. If it is not found, it will return null.

When data needs to be added to LruCache, LruCache will first determine whether the current cache size has reached the set maximum value. If it has reached the maximum value, the data at the end of the linked list will be deleted, and then the new data will be added to the head of the linked list and the hash table. If it has not reached the maximum value, the new data will be directly added to the head of the linked list and the hash table.

LruCache can effectively improve the performance of applications by managing cache data using a least recently used strategy.

LruCache usage scenarios

LruCache (Least Recently Used Cache) is a common cache strategy that determines which data is retained in the cache and which data is eliminated based on the order in which the data is accessed. LruCache is suitable for the following scenarios:

1. Memory Cache: LruCache can be used to cache frequently accessed data in memory, such as images, network request results, etc. By limiting the size of the cache, you can avoid memory overflow problems.
2. Database query result cache: When you need to query the database frequently and the query results do not change often, you can use LruCache to cache the query results to improve query performance.
3. Image loading: In Android development, LruCache is often used in the image loading framework, which can cache the loaded images to avoid repeated loading and waste of network resources.

LruCache is suitable for scenarios where you need to cache frequently accessed data and limit the cache size. It can improve the speed and performance of data access and avoid memory overflow problems.

LruCache Principle

1. LruCache is a data structure based on hash tables and doubly linked lists. The hash table is used to quickly find data in the cache, and the doubly linked list is used to maintain the access order of the data.
2. When new data is accessed, LruCache checks whether the data already exists in the cache. If it does, the data is moved to the head of the linked list to indicate that it has been recently accessed. If it does not exist, the data is added to the head of the linked list and the location of the data is recorded in the hash table.
3. When the cache reaches its maximum capacity, the longest unused data needs to be eliminated. LruCache removes the data at the end of the linked list and deletes the corresponding record from the hash table.
4. When data is accessed, if the data already exists in the cache, it is moved to the head of the linked list. This ensures that the data at the head of the linked list is the most recently accessed data, and the data at the tail of the linked list is the longest unused data.

LruCache can complete data search, insertion, and deletion operations in constant time, thereby improving cache efficiency.

LruCache usage

1. Create an LruCache object: Create an LruCache object through the constructor and specify the maximum capacity of the cache.
2. Adding objects to the cache: Use the put(key, value) method to add objects to the cache, where key is the unique identifier of the object and value is the object to be cached.
3. Get an object from the cache: Use the get(key) method to get an object from the cache. If the object exists, it returns the object; if the object does not exist, it returns null.
4. Remove an object from the cache: Use the remove(key) method to remove the object corresponding to the specified key from the cache.
5. Clear the cache: Use the evictAll() method to clear the cache and remove all objects from the cache.

Example code for using LruCache:

 // 创建LruCache对象，设置最大容量为10 LruCache<String, Bitmap> cache = new LruCache<>(10); // 添加对象到缓存cache.put("image1", bitmap1); cache.put("image2", bitmap2); // 从缓存中获取对象Bitmap image1 = cache.get("image1"); Bitmap image2 = cache.get("image2"); // 从缓存中移除对象cache.remove("image1"); // 清空缓存cache.evictAll();

By using LruCache, you can effectively manage cache objects in memory and improve application performance and responsiveness.