标签：android style blog color java os io strong
上一篇分析了LinkedHashMap源码，这个Map集合除了拥有HashMap的大部分特性之外，还拥有链表的特点，即可以保持遍历顺序与插入顺序一致。另外，当我们将accessOrder设置为true时，可以使遍历顺序和访问顺序一致，其内部双向链表将会按照近期最少访问到近期最多访问的顺序排列Entry对象，这可以用来做缓存。 private final LinkedHashMap<K, V> map;
/** Size of this cache in units. Not necessarily the number of elements. */
private int size;//当前大小
private int maxSize;//最大容量
private int putCount;//put次数
private int createCount;//create次数
private int evictionCount;//回收次数
private int hitCount;//命中次数
private int missCount;//丢失次数LinkedHashMap的初始化放在构造器中：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 put(K key, V value) {
if (key == null || value == null) {//键值不允许为空
throw new NullPointerException("key == null || value == null");
}
V previous;
synchronized (this) {//线程安全
putCount++;
size += safeSizeOf(key, value);
previous = map.put(key, value);
if (previous != null) {//之前已经插入过相同的key
size -= safeSizeOf(key, previous);//那么减去该entry的容量，因为发生覆盖
}
}
if (previous != null) {
entryRemoved(false, key, previous, value);//这个方法默认空实现
}
trimToSize(maxSize);//若容量超过maxsize，将会删除最近很少访问的entry
return previous;
}
public void trimToSize(int maxSize) {
while (true) {//不断删除linkedHashMap头部entry，也就是最近最少访问的条目，直到size小于最大容量
K key;
V value;
synchronized (this) {//线程安全
if (size < 0 || (map.isEmpty() && size != 0)) {
throw new IllegalStateException(getClass().getName()
+ ".sizeOf() is reporting inconsistent results!");
}
if (size <= maxSize || map.isEmpty()) {//直到容量小于最大容量为止
break;
}
Map.Entry<K, V> toEvict = map.entrySet().iterator().next();//指向链表头
key = toEvict.getKey();
value = toEvict.getValue();
map.remove(key);//删除最少访问的entry
size -= safeSizeOf(key, value);
evictionCount++;
}
entryRemoved(true, key, value, null);
}
}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 = null;
for (Map.Entry<K, V> entry : map.entrySet()) {
toEvict = entry;
}
if (toEvict == null) {
break;
}
key = toEvict.getKey();
value = toEvict.getValue();
map.remove(key);
size -= safeSizeOf(key, value);
evictionCount++;
}
entryRemoved(true, key, value, null);
}
}
public final V get(K key) {
if (key == null) {//不允许空键
throw new NullPointerException("key == null");
}
V mapValue;
synchronized (this) {//线程安全
mapValue = map.get(key);//调用LinkedHashMap的get方法
if (mapValue != null) {
hitCount++;//命中次数加1
return mapValue;//返回value
}
missCount++;//未命中
}
V createdValue = create(key);//默认返回为false
if (createdValue == null) {
return null;
}
synchronized (this) {
createCount++;//如果创建成功，那么create次数加1
mapValue = map.put(key, createdValue);//放到哈希表中
if (mapValue != null) {
// There was a conflict so undo that last 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 remove(K key) {
if (key == null) {
throw new NullPointerException("key == null");
}
V previous;
synchronized (this) {
previous = map.remove(key);//调用LinkedHashMap的remove方法
if (previous != null) {
size -= safeSizeOf(key, previous);
}
}
if (previous != null) {
entryRemoved(false, key, previous, null);
}
return previous;//返回value
} protected int sizeOf(K key, V value) {//用于计算每个条目的大小
return 1;
}snapshot方法，返回当前缓存中所有的条目集合 public synchronized final Map<K, V> snapshot() {
return new LinkedHashMap<K, V>(map);
}【源码】LruCache源码剖析,布布扣,bubuko.com
标签：android style blog color java os io strong
原文地址：http://blog.csdn.net/chdjj/article/details/38701509
