LruBuffer

java.lang.Object
- ohos.utils.LruBuffer<K,V>

类型参数:

K - Indicates the key type of the stored value.

V - Indicates the type of the stored value.
```
public class LruBuffer<K,V>
extends Object
```
A cache class that uses the least recently used (LRU) algorithm to remove the least recently accessed values when the capacity is insufficient for storing new values.
You can specify the capacity of a buffer. When the number of key-value pairs in the buffer exceeds its preset capacity, the LRU algorithm takes effect. Specifically, the least recently accessed key-value pairs will be removed to make room for new key-value pairs. You can also reset the buffer capacity. If the newly set buffer capacity is less than the number of already stored key-value pairs, the LRU algorithm is triggered to remove the least recently accessed key-value pairs. The following methods have an access token: put(java.lang.Object,java.lang.Object), get(java.lang.Object), contains(java.lang.Object).If one of them has been successfully called and has executed an actual operation for a value, this value will be marked as a recently accessed value and therefore its automatic clearance upon a full buffer will be postponed.
Most methods of this class support the synchronized mechanism and therefore can be used in multi-thread or concurrency scenarios. This class also provides the getMatchCount(), getMissCount(), and getPutCount() methods for you to obtain access statistics on stored key-value pairs, including the total numbers of matched queried key-value pairs, unmatched queried key-value pairs, and added key-value pairs.
In addition, you can override the afterRemoval(boolean,java.lang.Object,java.lang.Object,java.lang.Object) method in this class to perform subsequent operations after the stored key-value pairs are deleted or automatically cleared. Note: The buffer capacity cannot be set to 0, and the key or value cannot be null.

从以下版本开始:

2

构造器概要

构造器
构造器	说明
`LruBuffer()`	Default constructor used to create a new `LruBuffer` instance with the default capacity of 64.
`LruBuffer(int capacity)`	A constructor used to create a new `LruBuffer` instance.

方法概要

所有方法实例方法具体方法
限定符和类型	方法	说明
`protected void`	`afterRemoval(boolean isEvict, K key, V value, V newValue)`	Executes subsequent operations after a value is deleted.
`int`	`capacity()`	Obtains the capacity of the current buffer.
`void`	`clear()`	Clears key-value pairs from the current buffer.
`boolean`	`contains(K key)`	Checks whether the current buffer contains a specified key.
`protected V`	`createDefault(K key)`	Executes subsequent operations if miss to compute a value for the specific key.
`V`	`get(K key)`	Obtains the value associated with a specified key.
`int`	`getCreateCount()`	Obtains the number of times `createDefault(java.lang.Object)` returned a value.
`int`	`getMatchCount()`	Obtains the number of times that the queried values are successfully matched.
`int`	`getMissCount()`	Obtains the number of times that the queried values are not matched.
`int`	`getPutCount()`	Obtains the number of times that values are added to the buffer.
`int`	`getRemovalCount()`	Obtains the number of times that values are evicted from the buffer.
`boolean`	`isEmpty()`	Checks whether the current buffer is empty.
`List<K>`	`keys()`	Obtains a list of keys for the values in the current buffer.
`V`	`put(K key, V value)`	Adds a key-value pair to the buffer.
`Optional<V>`	`remove(K key)`	Deletes a specified `key` and its associated value from the current buffer.
`int`	`size()`	Obtains the total number of values in the current buffer.
`String`	`toString()`	Returns a string representation of the object.
`void`	`updateCapacity(int newCapacity)`	Updates the buffer capacity to a specified capacity.
`List<V>`	`values()`	Obtains a list of all values in the current buffer.

从类继承的方法 java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- 构造器详细资料
  - LruBuffer
```
public LruBuffer()
```
    Default constructor used to create a new LruBuffer instance with the default capacity of 64.
    
    从以下版本开始:
    
    2
  - LruBuffer
```
public LruBuffer(int capacity)
```
    A constructor used to create a new LruBuffer instance.
    
    参数:
    
    capacity - Indicates the capacity to customize for the buffer.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if capacity is less than or equal to 0.
    
    从以下版本开始:
    
    2
- 方法详细资料
  - afterRemoval
```
protected void afterRemoval(boolean isEvict,
                            K key,
                            V value,
                            V newValue)
```
    Executes subsequent operations after a value is deleted.
    This method is automatically called when the remove(java.lang.Object), clear(), put(java.lang.Object,java.lang.Object), or updateCapacity(int) method is used. You can determine whether to override this method based on the features of the stored value.
    
    参数:
    
    isEvict - The parameter value is true if this method is called due to insufficient capacity, and the parameter value is false in other cases.
    
    key - Indicates the deleted key.
    
    value - Indicates the deleted value.
    
    newValue - The parameter value is the new value associated if the put(java.lang.Object,java.lang.Object) method is called and the key to add already exists. The parameter value is null in other cases.
    
    从以下版本开始:
    
    2
  - createDefault
```
protected V createDefault(K key)
```
    Executes subsequent operations if miss to compute a value for the specific key.
    This method is automatically called if after get(java.lang.Object) miss to compute a value for the key. You can determine whether to override this method based on the features of the stored value.
    
    参数:
    
    key - Indicates the missed key.
    
    返回:
    
    Returns the value associated with the key.
    
    从以下版本开始:
    
    3
  - capacity
```
public final int capacity()
```
    Obtains the capacity of the current buffer.
    
    返回:
    
    Returns the capacity of the current buffer.
    
    从以下版本开始:
    
    2
  - clear
```
public final void clear()
```
    Clears key-value pairs from the current buffer. When the key-value pairs are cleared, the afterRemoval(boolean,java.lang.Object,java.lang.Object,java.lang.Object) method is called to execute subsequent operations for them in sequence.
    
    从以下版本开始:
    
    2
  - getMatchCount
```
public final int getMatchCount()
```
    Obtains the number of times that the queried values are successfully matched.
    
    返回:
    
    Returns the number of times that the queried values are successfully matched.
    
    从以下版本开始:
    
    2
  - getMissCount
```
public final int getMissCount()
```
    Obtains the number of times that the queried values are not matched.
    
    返回:
    
    Returns the number of times that the queried values are not matched.
    
    从以下版本开始:
    
    2
  - getPutCount
```
public final int getPutCount()
```
    Obtains the number of times that values are added to the buffer.
    
    返回:
    
    Returns the number of times that values are added to the buffer.
    
    从以下版本开始:
    
    2
  - contains
```
public final boolean contains(K key)
```
    Checks whether the current buffer contains a specified key.
    
    参数:
    
    key - Indicates the key to check.
    
    返回:
    
    Returns true if the buffer contains the specified key.
    
    从以下版本开始:
    
    2
  - get
```
public final V get(K key)
```
    Obtains the value associated with a specified key.
    
    参数:
    
    key - Indicates the key to query.
    
    返回:
    
    Returns the value associated with the key if the specified key is present in the buffer; returns null otherwise.
    
    从以下版本开始:
    
    2
  - getCreateCount
```
public final int getCreateCount()
```
    Obtains the number of times createDefault(java.lang.Object) returned a value.
    
    返回:
    
    Returns the number of times createDefault(java.lang.Object) returned a value.
    
    从以下版本开始:
    
    3
  - isEmpty
```
public final boolean isEmpty()
```
    Checks whether the current buffer is empty.
    
    返回:
    
    Returns true if the current buffer contains no value.
    
    从以下版本开始:
    
    2
  - keys
```
public final List<K> keys()
```
    Obtains a list of keys for the values in the current buffer.
    
    返回:
    
    Returns a list of keys sorted from most recently accessed to least recently accessed.
    
    从以下版本开始:
    
    2
  - put
```
public final V put(K key,
                   V value)
```
    Adds a key-value pair to the buffer.
    If the current buffer is full, the least recently accessed key-value pair will be automatically cleared to make room for adding the new key-value pair. If the key to be added already exists in the buffer, its associated value will be replaced by value to be added.
    
    参数:
    
    key - Indicates the key to add.
    
    value - Indicates the value associated with the key to add.
    
    返回:
    
    Returns the value associated with the added key; returns the original value if the key to add already exists.
    
    抛出:
    
    NullPointerException - Throws this exception if key or value is null.
    
    从以下版本开始:
    
    2
  - getRemovalCount
```
public final int getRemovalCount()
```
    Obtains the number of times that values are evicted from the buffer.
    
    返回:
    
    Returns the number of times that values are evicted from the buffer.
    
    从以下版本开始:
    
    3
  - remove
```
public final Optional<V> remove(K key)
```
    Deletes a specified key and its associated value from the current buffer.
    After the associated value is deleted, the afterRemoval(boolean,java.lang.Object,java.lang.Object,java.lang.Object) method is automatically called to perform subsequent operations for the deleted value.
    
    参数:
    
    key - Indicates the key to delete.
    
    返回:
    
    Returns an Optional object containing the deleted key-value pair; returns an empty Optional object if the key does not exist.
    
    抛出:
    
    NullPointerException - Throws this exception if key is null.
    
    从以下版本开始:
    
    2
  - size
```
public final int size()
```
    Obtains the total number of values in the current buffer.
    
    返回:
    
    Returns the total number of values in the current buffer.
    
    从以下版本开始:
    
    2
  - toString
```
public String toString()
```
    从类复制的说明: Object
    Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.
    The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:
    getClass().getName() + '@' + Integer.toHexString(hashCode())
    覆盖:
    
    toString 在类中 Object
    
    返回:
    
    a string representation of the object.
  - updateCapacity
```
public final void updateCapacity(int newCapacity)
```
    Updates the buffer capacity to a specified capacity.
    If the specified capacity is less than the total number of values stored in the buffer, values are cleared based on their access frequency from least recently accessed to most recently accessed, until the number equals to the specified capacity.
    
    参数:
    
    newCapacity - Indicates the new capacity to set.
    
    抛出:
    
    IllegalArgumentException - Throws this exception if newCapacity is less than or equal to 0.
    
    从以下版本开始:
    
    2
  - values
```
public final List<V> values()
```
    Obtains a list of all values in the current buffer.
    
    返回:
    
    Returns the list of all values in the current buffer in ascending order, from the most recently accessed to least recently accessed.
    
    从以下版本开始:
    
    2

类 LruBuffer<K,V>

构造器概要

方法概要

从类继承的方法 java.lang.Object

构造器详细资料

LruBuffer

LruBuffer

方法详细资料

afterRemoval

createDefault

capacity

clear

getMatchCount

getMissCount

getPutCount

contains

get

getCreateCount

isEmpty

keys

put

getRemovalCount

remove

size

toString

updateCapacity

values