文章目录
1、LinkedHashMap的主要成员变量及构造
public class LinkedHashMap<K,V>
extends HashMap<K,V>
implements Map<K,V> {
// 双向链表的头部
transient LinkedHashMap.Entry<K,V> head;
// 双向链表的尾部
transient LinkedHashMap.Entry<K,V> tail;
// 此链接哈希映射的迭代排序方法:true用于访问顺序，false用于插入顺序
final boolean accessOrder;
public LinkedHashMap(int initialCapacity, float loadFactor) {
super(initialCapacity, loadFactor);
accessOrder = false;
}
public LinkedHashMap(int initialCapacity) {
super(initialCapacity);
accessOrder = false;
}
public LinkedHashMap() {
super();
accessOrder = false;
}
public LinkedHashMap(Map<? extends K, ? extends V> m) {
super();
accessOrder = false;
putMapEntries(m, false);
}
public LinkedHashMap(int initialCapacity,float loadFactor,boolean accessOrder) {
super(initialCapacity, loadFactor);
this.accessOrder = accessOrder;
}
...........................
}
2、get通过键名查找定的数据
// 使用了HashMap中的内部类
static class Node<K,V> implements Map.Entry<K,V> {
final int hash;
final K key;
V value;
Node<K,V> next;
Node(int hash, K key, V value, Node<K,V> next) {
this.hash = hash;
this.key = key;
this.value = value;
this.next = next;
}
...................
}
public V get(Object key) {
Node<K,V> e;
// 使用了HashMap中的getNode方法查询对应的节点
if ((e = getNode(hash(key), key)) == null)
return null;
if (accessOrder)
afterNodeAccess(e);
return e.value;
}
3、put、replace、remove，由于该类没有重写对应的put、replace、remove方法，所以引用父类HashMap的方法，但是对应的功能方法里面执行的方法却有重写
void reinitialize() {
super.reinitialize();
head = tail = null;
}
Node<K,V> newNode(int hash, K key, V value, Node<K,V> e) {
LinkedHashMap.Entry<K,V> p =
new LinkedHashMap.Entry<K,V>(hash, key, value, e);
linkNodeLast(p);
return p;
}
Node<K,V> replacementNode(Node<K,V> p, Node<K,V> next) {
LinkedHashMap.Entry<K,V> q = (LinkedHashMap.Entry<K,V>)p;
LinkedHashMap.Entry<K,V> t =
new LinkedHashMap.Entry<K,V>(q.hash, q.key, q.value, next);
transferLinks(q, t);
return t;
}
TreeNode<K,V> newTreeNode(int hash, K key, V value, Node<K,V> next) {
TreeNode<K,V> p = new TreeNode<K,V>(hash, key, value, next);
linkNodeLast(p);
return p;
}
TreeNode<K,V> replacementTreeNode(Node<K,V> p, Node<K,V> next) {
LinkedHashMap.Entry<K,V> q = (LinkedHashMap.Entry<K,V>)p;
TreeNode<K,V> t = new TreeNode<K,V>(q.hash, q.key, q.value, next);
transferLinks(q, t);
return t;
}
4、containsValue查询是否存在对应的Value值
public boolean containsValue(Object value) {
for (LinkedHashMap.Entry<K,V> e = head; e != null; e = e.after) {
V v = e.value;
if (v == value || (value != null && value.equals(v)))
return true;
}
return false;
}
5、clear清空
public void clear() {
super.clear();
head = tail = null;
}
6、LinkedHashMap与HashMap的关联
在HashMap类中可以看到有三个方法如下，没有实现方法体，但是在LinkedHashMap类中这三个方法有方法体，有对应的实现，该注释说明了允许LinkedHashMap的后期回调
在LinkedHashMap中这三个方法对应的重写方法
void afterNodeRemoval(Node<K,V> e) { // unlink
LinkedHashMap.Entry<K,V> p =
(LinkedHashMap.Entry<K,V>)e, b = p.before, a = p.after;
p.before = p.after = null;
if (b == null)
head = a;
else
b.after = a;
if (a == null)
tail = b;
else
a.before = b;
}
void afterNodeInsertion(boolean evict) { // possibly remove eldest
LinkedHashMap.Entry<K,V> first;
if (evict && (first = head) != null && removeEldestEntry(first)) {
K key = first.key;
removeNode(hash(key), key, null, false, true);
}
}
void afterNodeAccess(Node<K,V> e) { // move node to last
LinkedHashMap.Entry<K,V> last;
if (accessOrder && (last = tail) != e) {
LinkedHashMap.Entry<K,V> p =
(LinkedHashMap.Entry<K,V>)e, b = p.before, a = p.after;
p.after = null;
if (b == null)
head = a;
else
b.after = a;
if (a != null)
a.before = b;
else
last = b;
if (last == null)
head = p;
else {
p.before = last;
last.after = p;
}
tail = p;
++modCount;
}
}
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