例如對網絡加載圖片進行緩存：
// 得到應用程序被分配的最大的內存int maxMemory=(int) Runtime.getRuntime().maxMemory(); // 取處內存的1/5 用來當緩存大小int cachSize=maxMemory/5; // 實例化LruCache lruCache=new lruCache<String, Bitmap>(cachSize){ //內部方法sizeOf設置每一張圖片的緩存大小protected int sizeOf(String key, Bitmap value) { //在每次存入緩存時調用，告訴系統這張緩存圖片有多大// 相當於為每次要緩存的資源分配大小空間return value.getByteCount(); } };上面的代碼一般放在初始化的方法裡面
其實可以將LurCache 類理解為Map 類map 有put和get 方法
接下去就調用put 和get 方法進行需要緩存資源的存取
LurCache 的add ：
public void putBitmapToCache(String url,Bitmap bitmap){ if (getBitmapfromCache(url)==null) {//判斷當前緩存是否存在lruCache.put(url, bitmap); } }LurCache 的get：public Bitmap getBitmapfromCache(String url){ return lruCache.get(url);//可將lruCache看成map }調用上面的add 和get 方法就可以對資源進行緩存的，還是挺簡單的，
但要注意一點LruCache lruCache=new LruCache<String, Bitmap>(cachSize)只能被new 一次，不然不同對象就不同的緩存了
附上Android的Lrucache類
package android.util; import java.util.LinkedHashMap; import java.util.Map; /** * 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。 * 當cache已滿的時候加入新的item時，在隊列尾部的item會被回收。 * <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* 大小。 * <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. * 不允許key或者value為null * 當get（），put（），remove（）返回值為null時，key相應的項不在cache中*/ public class LruCache<K, V> { private final LinkedHashMap<K, V> map; /** Size of this cache in units. Not necessarily the number of elements. */ private int size; //已經存儲的大小private int maxSize; //規定的最大存儲空間private int putCount; //put的次數private int createCount; //create的次數private int evictionCount; //回收的次數private int hitCount; //命中的次數private int 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. */ public LruCache(int maxSize) { if (maxSize <= 0) { throw new IllegalArgumentException("maxSize <= 0"); } this.maxSize = maxSize; this.map = new LinkedHashMap<K, V>(0, 0.75f, 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， * 如果item的value沒有被cache或者不能被創建，則返回null。 */ public final V get(K key) { if (key == null) { throw new NullPointerException("key == null"); } V mapValue; synchronized (this) { mapValue = map.get(key); if (mapValue != null) { hitCount++; //命中return mapValue; } missCount++; //丟失} /* * 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 */ V createdValue = create(key); if (createdValue == null) { return null; } synchronized (this) { createCount++;//創建++ mapValue = map.put(key, createdValue); if (mapValue != null) { // There was a conflict so undo that last put //如果前面存在oldValue，那麼撤銷put（） map.put(key, mapValue); } else { size += safeSizeOf(key, createdValue); } } if (mapValue != null) { entryRemoved(false, key, createdValue, mapValue); return mapValue; } else { trimToSize(maxSize); return createdValue; } } /** * Caches {@code value} for {@code key}. The value is moved to the head of * the queue. * * @return the previous value mapped by {@code key}. */ public final V put(K key, V value) { if (key == null || value == null) { throw new NullPointerException("key == null || value == null"); } V previous; synchronized (this) { putCount++; size += safeSizeOf(key, value); previous = map.put(key, value); if (previous != null) { //返回的先前的value值size -= safeSizeOf(key, previous); } } if (previous != null) { entryRemoved(false, key, previous, value); } trimToSize(maxSize); return previous; } /** * @param maxSize the maximum size of the cache before returning. May be -1 * to evict even 0-sized elements. * 清空cache空間*/ private void trimToSize(int maxSize) { while (true) { K key; V value; synchronized (this) { if (size < 0 || (map.isEmpty() && size != 0)) { throw new IllegalStateException(getClass().getName() + ".sizeOf() is reporting inconsistent results!"); } if (size <= maxSize) { break; } Map.Entry<K, V> toEvict = map.eldest(); if (toEvict == null) { break; } key = toEvict.getKey(); value = toEvict.getValue(); map.remove(key); size -= safeSizeOf(key, value); evictionCount++; } entryRemoved(true, key, value, null); } } /** * 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}. */ public final V remove(K key) { if (key == null) { throw new NullPointerException("key == null"); } V previous; synchronized (this) { previous = map.remove(key); if (previous != null) { size -= safeSizeOf(key, previous); } } if (previous != null) { entryRemoved(false, key, previous, null); } return previous; } /** * 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， * 或者替換item值時put調用，默認實現什麼都沒做。 * <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}. * true---為釋放空間被刪除；false---put或remove導致* @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}. */ protected void entryRemoved(boolean evicted, K key, V oldValue, V newValue) {} /** * 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 V create(K key) { return null; } private int safeSizeOf(K key, V value) { int result = sizeOf(key, value); if (result < 0) { throw new IllegalStateException("Negative size: " + key + "=" + value); } return result; } /** * 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. */ protected int sizeOf(K key, V value) { return 1; } /** * Clear the cache, calling {@link #entryRemoved} on each removed entry. * 清空cacke */ public final void evictAll() { trimToSize(-1); // -1 will evict 0-sized elements } /** * 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. */ public synchronized final int size() { return size; } /** * 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. */ public synchronized final int maxSize() { return maxSize; } /** * Returns the number of times {@link #get} returned a value that was * already present in the cache. */ public synchronized final int hitCount() { return hitCount; } /** * Returns the number of times {@link #get} returned null or required a new * value to be created. */ public synchronized final int missCount() { return missCount; } /** * Returns the number of times {@link #create(Object)} returned a value. */ public synchronized final int createCount() { return createCount; } /** * Returns the number of times {@link #put} was called. */ public synchronized final int putCount() { return putCount; } /** * Returns the number of values that have been evicted. * 返回被回收的數量*/ public synchronized final int evictionCount() { return evictionCount; } /** * 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*/ public synchronized final Map<K, V> snapshot() { return new LinkedHashMap<K, V>(map); } @Override public synchronized final String toString() { int accesses = hitCount + missCount; int hitPercent = accesses != 0 ? (100 * hitCount / accesses) : 0; return String.format("LruCache[maxSize=%d,hits=%d,misses=%d,hitRate=%d%%]", maxSize, hitCount, missCount, hitPercent); } }