LruCache
A cache that holds strong references to a limited number of values. Each time a value is accessed, it is moved to the head of a queue. When a value is added to a full cache, the value at the end of that queue is evicted and may become eligible for garbage collection.
If your cached values hold resources that need to be explicitly released, override entryRemoved.
If a cache miss should be computed on demand for the corresponding keys, override create. This simplifies the calling code, allowing it to assume a value will always be returned, even when there's a cache miss.
By default, the cache size is measured in the number of entries. Override sizeOf to size the cache in different units. For example, this cache is limited to 4MiB of bitmaps:
val cacheSize = 4 * 1024 * 1024; // 4MiB
val bitmapCache = LruCache<String, Bitmap>(cacheSize) {
override fun sizeOf(key: String, value: Bitmap) = value.byteCount
}
This class is thread-safe.
This class does not allow null to be used as a key or value. A return value of null from get, put or remove is unambiguous: the key was not in the cache.
Summary
Public constructors |
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Creates a new |
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Public functions |
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Int |
Returns the number of times |
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Unit |
evictAll()Clear the cache, calling |
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Int |
Returns the number of values that have been evicted. |
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operator V? |
get(key: K)Returns the value for |
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Int |
hitCount()Returns the number of times |
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Int |
maxSize()For caches that do not override |
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Int |
Returns the number of times |
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V? |
put(key: K, value: V) |
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Int |
putCount()Returns the number of times |
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V? |
remove(key: K)Removes the entry for |
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open Unit |
Sets the size of the cache. |
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Int |
size()For caches that do not override |
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MutableMap<K, V> |
snapshot()Returns a mutable copy of the current contents of the cache, ordered from least recently accessed to most recently accessed. |
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open String |
toString() |
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open Unit |
trimToSize(maxSize: Int)Remove the eldest entries until the total of remaining entries is at or below the requested size. |
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Protected functions |
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open V? |
create(key: K)Called after a cache miss to compute a value for the corresponding key. |
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open Unit |
entryRemoved(evicted: Boolean, key: K, oldValue: V, newValue: V?)Called for entries that have been evicted or removed. |
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open Int |
sizeOf(key: K, value: V)Returns the size of the entry for |
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Public functions
get
operator fun get(key: K): V?
Returns the value for key if it exists in the cache or can be created by create. If a value was returned, it is moved to the head of the queue. This returns null if a value is not cached and cannot be created.
hitCount
fun hitCount(): Int
Returns the number of times get returned a value that was already present in the cache.
maxSize
fun maxSize(): Int
For caches that do not override sizeOf, this returns the maximum number of entries in the cache. For all other caches, this returns the maximum sum of the sizes of the entries in this cache.
missCount
fun missCount(): Int
Returns the number of times get returned null or required a new value to be created.
put
fun put(key: K, value: V): V?
Caches value for key. The value is moved to the head of the queue.
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V? |
the previous value mapped by |
remove
fun remove(key: K): V?
Removes the entry for key if it exists.
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V? |
the previous value mapped by |
resize
open fun resize(maxSize: @IntRange(from = 1, to = 2147483647) Int): Unit
Sets the size of the cache.
size
fun size(): Int
For caches that do not override sizeOf, this returns the number of entries in the cache. For all other caches, this returns the sum of the sizes of the entries in this cache.
snapshot
fun snapshot(): MutableMap<K, V>
Returns a mutable copy of the current contents of the cache, ordered from least recently accessed to most recently accessed.
trimToSize
open fun trimToSize(maxSize: Int): Unit
Remove the eldest entries until the total of remaining entries is at or below the requested size.
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maxSize: Int |
the maximum size of the cache before returning. May be -1 to evict even 0-sized elements. |
Protected functions
create
protected open fun create(key: K): V?
Called after a cache miss to compute a value for the corresponding key. Returns the computed value or null if no value can be computed. The default implementation returns null.
The method is called without synchronization: other threads may access the cache while this method is executing.
If a value for key exists in the cache when this method returns, the created value will be released with entryRemoved and discarded. This can occur when multiple threads request the same key at the same time (causing multiple values to be created), or when one thread calls put while another is creating a value for the same key.
entryRemoved
protected open fun entryRemoved(evicted: Boolean, key: K, oldValue: V, newValue: V?): Unit
Called for entries that have been evicted or removed. This method is invoked when a value is evicted to make space, removed by a call to remove, or replaced by a call to put. The default implementation does nothing.
The method is called without synchronization: other threads may access the cache while this method is executing.
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evicted: Boolean |
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key: K |
key of the entry that was evicted or removed. |
oldValue: V |
the original value of the entry that was evicted removed. |
newValue: V? |
the new value for |
sizeOf
protected open fun sizeOf(key: K, value: V): Int
Returns the size of the entry for key and value in user-defined units. The default implementation returns 1 so that size is the number of entries and max size is the maximum number of entries.
An entry's size must not change while it is in the cache.