分類： Android開發 2013-02-06 15:26 26733人閱讀 評論(10) 收藏 舉報

package?android.util; ?

import import /**?

?*?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.?

?*?Cache保存一個強引用來限制內容數量，每當Item被訪問的時候，此Item就會移動到隊列的頭部。

?*?<p>If?your?cached?values?hold?resources?that?need?to?be?explicitly?released,?

?*?override?{@link?#entryRemoved}.?

?*?如果你cache的某個值需要明確釋放，重寫entryRemoved()

?*?<p>If?a?cache?miss?should?be?computed?on?demand?for?the?corresponding?keys,?

?*?override?{@link?#create}.?This?simplifies?the?calling?code,?allowing?it?to?

?*?assume?a?value?will?always?be?returned,?even?when?there's?a?cache?miss.?

?*?如果key相對應的item丟掉啦，重寫create().這簡化了調用代碼，即使丟失了也總會返回。

?*?<p>By?default,?the?cache?size?is?measured?in?the?number?of?entries.?Override?

?*?{@link?#sizeOf}?to?size?the?cache?in?different?units.?For?example,?this?cache?

?*?is?limited?to?4MiB?of?bitmaps:?默認cache大小是測量的item的數量，重寫sizeof計算不同item的

?*?<pre>???{@code?

?*???int?cacheSize?=?4?*?1024?*?1024;?//?4MiB?

?*???LruCache<String,?Bitmap>?bitmapCache?=?new?LruCache<String,?Bitmap>(cacheSize)?{?

?*???????protected?int?sizeOf(String?key,?Bitmap?value)?{?

?*???????????return?value.getByteCount();?

?*???????}?

?*???}}</pre>?

?*?

?*?<p>This?class?is?thread-safe.?Perform?multiple?cache?operations?atomically?by?

?*?synchronizing?on?the?cache:?<pre>???{@code?

?*???synchronized?(cache)?{?

?*?????if?(cache.get(key)?==?null)?{?

?*?????????cache.put(key,?value);?

?*?????}?

?*???}}</pre>?

?*?

?*?<p>This?class?does?not?allow?null?to?be?used?as?a?key?or?value.?A?return?

?*?value?of?null?from?{@link?#get},?{@link?#put}?or?{@link?#remove}?is?

?*?unambiguous:?the?key?was?not?in?the?cache.

?*/ publicclass privatefinal ??

privateint?size; //已經存儲的大小

privateint?maxSize; //規定的最大存儲空間

privateint?putCount; ?//put的次數

privateint?createCount; ?//create的次數

privateint?evictionCount; ?//回收的次數

privateint?hitCount; ?//命中的次數

privateint?missCount; ?//丟失的次數

?????*?@param?maxSize?for?caches?that?do?not?override?{@link?#sizeOf},?this?is?

?????*?????the?maximum?number?of?entries?in?the?cache.?For?all?other?caches,?

?????*?????this?is?the?maximum?sum?of?the?sizes?of?the?entries?in?this?cache.?

?????*/ publicint if)?{??

thrownew this thisnew,?.75f,?true ?????*?Returns?the?value?for?{@code?key}?if?it?exists?in?the?cache?or?can?be?

?????*?created?by?{@code?#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.?通過key返回相應的item，或者創建返回相應的item。相應的item會移動到隊列的頭部，

?????*/ publicfinal ifnull thrownew synchronizedthis ifnull return ?????????*?Attempt?to?create?a?value.?This?may?take?a?long?time,?and?the?map?

?????????*?may?be?different?when?create()?returns.?If?a?conflicting?value?was?

?????????*?added?to?the?map?while?create()?was?working,?we?leave?that?value?in?

?????????*?the?map?and?release?the?created?value.?

?????????* 如果丟失了就試圖創建一個item

? ? ? ? ?*/ ifnull returnnull synchronizedthis ifnull ??

? ? ? ? ? ? ? ? //如果前面存在oldValue，那么撤銷put（）?

else ifnull false return else return ?????*?Caches?{@code?value}?for?{@code?key}.?The?value?is?moved?to?the?head?of?

?????*?the?queue.?

?????*?

?????*?@return?the?previous?value?mapped?by?{@code?key}.?

?????*/ publicfinal ifnullnull thrownew synchronizedthis ifnull)?{ ?//返回的先前的value值

ifnull false return ?????*?@param?maxSize?the?maximum?size?of?the?cache?before?returning.?May?be?-1?

?????*?????to?evict?even?0-sized?elements.?

?????*/ privatevoidint whiletrue synchronizedthis if?||?(map.isEmpty()?&&?size?!=?))?{??

thrownew if break ifnull break truenull ?????*?Removes?the?entry?for?{@code?key}?if?it?exists.?

?????*?刪除key相應的cache項，返回相應的value

?????*?@return?the?previous?value?mapped?by?{@code?key}.?

?????*/ publicfinal ifnull thrownew synchronizedthis ifnull ifnull falsenull return ?????*?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?

?????*?{@link?#remove},?or?replaced?by?a?call?to?{@link?#put}.?The?default?

?????*?implementation?does?nothing.?

?????*?當item被回收或者刪掉時調用。改方法當value被回收釋放存儲空間時被remove調用，

?????*?<p>The?method?is?called?without?synchronization:?other?threads?may?

?????*?access?the?cache?while?this?method?is?executing.?

?????*?

?????*?@param?evicted?true?if?the?entry?is?being?removed?to?make?space,?false?

?????*?????if?the?removal?was?caused?by?a?{@link?#put}?or?{@link?#remove}.?

?????*?@param?newValue?the?new?value?for?{@code?key},?if?it?exists.?If?non-null,?

?????*?????this?removal?was?caused?by?a?{@link?#put}.?Otherwise?it?was?caused?by?

?????*?????an?eviction?or?a?{@link?#remove}.?

?????*/ protectedvoidboolean ?????*?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.?

?????*?當某Item丟失時會調用到，返回計算的相應的value或者null

?????*?<p>The?method?is?called?without?synchronization:?other?threads?may?

?????*?access?the?cache?while?this?method?is?executing.?

?????*?

?????*?<p>If?a?value?for?{@code?key}?exists?in?the?cache?when?this?method?

?????*?returns,?the?created?value?will?be?released?with?{@link?#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?{@link?#put}?while?another?is?creating?a?value?for?the?same?

?????*?key.?

?????*/ protected returnnull privateint int if)?{??

thrownew?+?value);??

return ?????*?Returns?the?size?of?the?entry?for?{@code?key}?and?{@code?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.?

?????*?返回用戶定義的item的大小，默認返回1代表item的數量，最大size就是最大item值

?????*?<p>An?entry's?size?must?not?change?while?it?is?in?the?cache.?

?????*/ protectedint return;??

?????*?Clear?the?cache,?calling?{@link?#entryRemoved}?on?each?removed?entry.?

?????*/ publicfinalvoid );???

?????*?For?caches?that?do?not?override?{@link?#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.?

?????*/ publicsynchronizedfinalint return ?????*?For?caches?that?do?not?override?{@link?#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.?

?????*/ publicsynchronizedfinalint return ?????*?Returns?the?number?of?times?{@link?#get}?returned?a?value?that?was?

?????*?already?present?in?the?cache.?

?????*/ publicsynchronizedfinalint return ?????*?Returns?the?number?of?times?{@link?#get}?returned?null?or?required?a?new?

?????*?value?to?be?created.?

?????*/ publicsynchronizedfinalint return ?????*?Returns?the?number?of?times?{@link?#create(Object)}?returned?a?value.?

?????*/ publicsynchronizedfinalint return ?????*?Returns?the?number?of?times?{@link?#put}?was?called.?

?????*/ publicsynchronizedfinalint return ?????*?Returns?the?number?of?values?that?have?been?evicted.?

?????*/ publicsynchronizedfinalint return ?????*?Returns?a?copy?of?the?current?contents?of?the?cache,?ordered?from?least?

?????*?recently?accessed?to?most?recently?accessed.?返回當前cache的副本，從最近最少訪問到最多訪問

?????*/ publicsynchronizedfinal returnnew ?publicsynchronizedfinal int int???(?*?hitCount?/?accesses)?:?;??

return,??

}?

轉載于:https://www.cnblogs.com/xgjblog/p/4064806.html

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