Android LruCache类分析 _lrucache

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public class LurCache< K, V> { private final LinkedHashMap< K, V> map; private int size; // 已经存储的大小 private int maxSize; // 规定的最大存储空间 private int putCount; // put的次数 private int createCount; // create的次数 private int evictionCount; // 回收的次数 private int hitCount; // 命中的次数 private int missCount; // 丢失的次数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); }public final V get(K key) { if (key == null) { throw new NullPointerException("key == null"); }V mapValue; synchronized (this) { mapValue = https://www.songbingjia.com/android/map.get(key); if (mapValue != null) { hitCount++; // 命中 return mapValue; } missCount++; // 丢失 }V createdValue = create(key); if (createdValue == null) { return null; }synchronized (this) { createCount++; // 创建++ mapValue = map.put(key, createdValue); if (mapValue != null) { // There was a conflict so undo that last put // 如果前面存在oldValue，那么撤销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; } }public final V put(K key, V value) { if (key == null || value == null) { throw new NullPointerException("key == null || value =https://www.songbingjia.com/android/= 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; } //清空cache空间 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.entrySet().iterator().next(); if (toEvict == null) { break; }key = toEvict.getKey(); value = https://www.songbingjia.com/android/toEvict.getValue(); map.remove(key); size -= safeSizeOf(key, value); evictionCount++; }entryRemoved(true, key, value, null); } } //删除key相应的cache项，返回相应的value 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; } //当item被回收或者删掉时调用。该方法当value被回收释放存储空间时被remove调用，或者替换item值时put调用，默认实现什么都没做。 //true: 为释放空间被删除；false: put或remove导致 protected void entryRemoved(boolean evicted, K key, V oldValue, V newValue) {} 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; }protected int sizeOf(K key, V value) { return 1; } //清空cache public final void evictAll() { trimToSize(-1); // -1 will evict 0-sized elements }public synchronized final int size() { return size; }public synchronized final int maxSize() { return maxSize; }public synchronized final int hitCount() { return hitCount; }public synchronized final int missCount() { return missCount; }public synchronized final int createCount() { return createCount; }public synchronized final int putCount() { return putCount; }//返回被回收的数量 public synchronized final int evictionCount() { return evictionCount; } //返回当前cache的副本，从最近最少访问到最多访问 public synchronized final Map< K, V> snapshot() { return new LinkedHashMap< K, V> (map); }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); } }

【Android LruCache类分析】