首先呢？看这篇文章之前大家先对LinkedHashMap以及LruCache了解一下先，先看下面两篇文章哈：
Java LinkedHashMap工作原理及实现 | Yikun Android高效加载大图、多图解决方案，有效避免程序OOM - 博客
先会用再分析是最好的!!!
源码行动开始,看下面(到这里假设你已经是LinkedHashMap和LruCache有所了解的哦)
源码分析
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;
private int maxSize;
private int putCount;
private int createCount;
private int evictionCount;
private int hitCount;
private int missCount;
/**
* @param maxSize 缓存的最大值
*/
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);
}
/**
* 重新设置缓存最大值-跟调用trimToSize()方法效果一样的
*/
public void resize(int maxSize) {
if (maxSize <=
0) {
throw new IllegalArgumentException(
"maxSize <= 0");
}
synchronized (
this) {
this.maxSize = maxSize;
}
trimToSize(maxSize);
}
/**
* 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.
*/
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++;
return mapValue;
}
missCount++;
}
V createdValue = create(key);
if (createdValue ==
null) {
return null;
}
synchronized (
this) {
createCount++;
mapValue = map.put(key, createdValue);
if (mapValue !=
null) {
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) {
size -= safeSizeOf(key, previous);
}
}
if (previous !=
null) {
entryRemoved(
false, key, previous, value);
}
trimToSize(maxSize);
return previous;
}
/**
* Remove the eldest entries until the total of remaining entries is at or
* below the requested size.
*
* @param maxSize the maximum size of the cache before returning. May be -1
* to evict even 0-sized elements.
*/
public 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.
*
* @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.
*
* <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}.
*/
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.
*
* <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.
*
* <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.
*/
public
final void evictAll() {
trimToSize(-
1);
}
/**
* 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.
*/
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.
*/
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);
}
}
实战
看完了源码分析,肯定需要实践一下的,看这篇文章最后那里: LruCache详解之 Android 内存优化 - 博客
分析玩LruCache之后,希望你可以看看下面几篇文章: 1.Android高效加载大图、多图解决方案，有效避免程序OOM - 博客 2.Android DiskLruCache完全解析，硬盘缓存的最佳方案 - 博客 3. Android照片墙应用实现，再多的图片也不怕崩溃 - 博客
