LinkedHashMap

1.LinkedHashMap继承了HashMap并实现了Map接口

public class LinkedHashMap<K,V>    extends HashMap<K,V>    implements Map<K,V>

1.1LinkedHashMap中的元素变量

//双向链表的头结点
private transient Entry<K,V> header;
//true:最近最少使用次序
//false:表示遍历的时候根据插入的顺序
private final boolean accessOrder;

1.2LinkedHashMap的构造函数

//设置容量和加载因子
public LinkedHashMap(int initialCapacity, float loadFactor);
//只设置初始容量
public LinkedHashMap(int initialCapacity) ;
//使用默认值
public LinkedHashMap();

1.3LinkedHashMap是如何确认有序的

我们来看下节点代码的改动**

private static class Entry<K,V> extends HashMap.Entry<K,V> {
        Entry<K,V> before, after;

        Entry(int hash, K key, V value, HashMap.Entry<K,V> next) {
            super(hash, key, value, next);
        }

        private void remove() {
            before.after = after;
            after.before = before;
        }

        private void addBefore(Entry<K,V> existingEntry) {
            after  = existingEntry;
            before = existingEntry.before;
            before.after = this;
            after.before = this;
        }
        
        void recordAccess(HashMap<K,V> m) {
            LinkedHashMap<K,V> lm = (LinkedHashMap<K,V>)m;
            if (lm.accessOrder) {
                lm.modCount++;
                remove();
                addBefore(lm.header);
            }
        }
        void recordRemoval(HashMap<K,V> m) {
            remove();
        }
    }