1.定义变量accessOrder

public class LinkedHashMap<K,V> extends HashMap<K,V> implements Map<K,V> {final boolean accessOrder;public LinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder) {super(initialCapacity, loadFactor);this.accessOrder = accessOrder;}
}

2.最近访问的节点移动到链表末尾

 

public class LinkedHashMap<K,V> extends HashMap<K,V> implements Map<K,V> {void afterNodeAccess(Node<K,V> e) { // move node to lastLinkedHashMapEntry<K,V> last;if (accessOrder && (last = tail) != e) { //e不是tailLinkedHashMapEntry<K,V> p =(LinkedHashMapEntry<K,V>)e, b = p.before, a = p.after;p.after = null;if (b == null){ //原来p是head，p被移到最后，那head就变成p.afterhead = a;} else{b.after = a; //b  p  a 中间p被移走，b和a需要串起来}if (a != null){ //b  p  a 中间p被移走，b和a需要串起来a.before = b;} else{ //原来a为null，说明p为tail（这个场景不是不会走进来吗？）last = b;}if (last == null){ //last为null说明链表只有一个元素，更新headhead = p;}else {p.before = last; //last  plast.after = p;}tail = p; //更新尾++modCount;}}
}

3.LruCache

3.1.LruCache.put

public class LruCache<T, Y> {@Nullablepublic synchronized Y put(@NonNull T key, @Nullable Y item) {final int itemSize = getSize(item);if (itemSize >= maxSize) {onItemEvicted(key, item);return null;}if (item != null) {currentSize += itemSize;}@Nullable Entry<Y> old = cache.put(key, item == null ? null : new Entry<>(item, itemSize));if (old != null) {currentSize -= old.size;if (!old.value.equals(item)) {onItemEvicted(key, old.value);}}evict(); //看放入之后，大小是否超过return old != null ? old.value : null;}
}

3.2.LruCache.evict

public class LruCache<T, Y> {private void evict() {trimToSize(maxSize);}
}

3.3.LruCache.trimToSize

循环移除，直到size小于maxSize，每次移除链表头元素

public class LruCache<T, Y> {protected synchronized void trimToSize(long size) {Map.Entry<T, Entry<Y>> last;Iterator<Map.Entry<T, Entry<Y>>> cacheIterator;while (currentSize > size) {cacheIterator = cache.entrySet().iterator(); //LinkedHashMap遍历last = cacheIterator.next(); //获取的是链表的第一个元素final Entry<Y> toRemove = last.getValue();currentSize -= toRemove.size; //更新移除后的sizefinal T key = last.getKey();cacheIterator.remove();  //将元素移除onItemEvicted(key, toRemove.value);}}
}

3.4.LinkedHashIterator.remove

public class LinkedHashMap<K,V> extends HashMap<K,V> implements Map<K,V>{abstract class LinkedHashIterator {public final void remove() {Node<K,V> p = current;if (p == null){throw new IllegalStateException();}if (modCount != expectedModCount){throw new ConcurrentModificationException();}current = null;K key = p.key;removeNode(hash(key), key, null, false, false); //HashMap的移除方法expectedModCount = modCount;}}
}