tail.next = new Element;//簡單指定
newElement.prev = tail;
tail = newElement;

package com.hspedu.set_;
import java.util.LinkedHashSet;
import java.util.Set;
@SuppressWarnings({"all"})
public class LinkedHashSetSource {
    public static void main(String[] args) {
        //分析一下LinkedHashSet的底層機制
        Set set = new LinkedHashSet();
        set.add(new String("AA"));
        set.add(456);
        set.add(456);
        set.add(new Customer("劉", 1001));
        set.add(123);
        set.add("HSP");
        System.out.println("set=" + set);
        //老韓解讀
        //1. LinkedHashSet 加入順序和取出元素/數(shù)據(jù)的順序一致
        //2. LinkedHashSet 底層維護的是一個LinkedHashMap(是HashMap的子類)
        //3. LinkedHashSet 底層結構 (數(shù)組table+雙向鏈表)
        //4. 添加第一次時，直接將 數(shù)組table 擴容到 16 ,存放的結點類型是 LinkedHashMap$Entry
        //5. 數(shù)組是 HashMap$Node[] 存放的元素/數(shù)據(jù)是 LinkedHashMap$Entry類型
        /*
                //繼承關系是在內(nèi)部類完成.
                static class Entry<K,V> extends HashMap.Node<K,V> {
                    Entry<K,V> before, after;
                    Entry(int hash, K key, V value, Node<K,V> next) {
                        super(hash, key, value, next);
                    }
                }
         */
    }
}
class Customer {
    private String name;
    private int no;
    public Customer(String name, int no) {
        this.name = name;
        this.no = no;
    }
}

  LinkedHashSet set = new LinkedHashSet<>();
        set.add("湛江");
        set.add(null);
        set.add(168);
        set.add(new Date());
	步驟1：使用無參構造器創(chuàng)建對象
	public LinkedHashSet() {
        super(16, .75f, true); 調(diào)用父類的有參構造 HashSet 在底層創(chuàng)建一個 LinkedHashMap
      }
    HashSet(int initialCapacity, float loadFactor, boolean dummy) {
        map = new LinkedHashMap<>(initialCapacity, loadFactor);
    }  
    在 LinkedHashMap 的構造器調(diào)用父類的 構造器 HashMap  注意是：LinkedHashMap是HashMap的子類
    public LinkedHashMap(int initialCapacity, float loadFactor) {
        super(initialCapacity, loadFactor);loadFactor加載因子   initialCapacity初始容量
        accessOrder = false;
    }
       public HashMap(int initialCapacity, float loadFactor) {
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal initial capacity: " +
                                               initialCapacity);
        if (initialCapacity > MAXIMUM_CAPACITY)
            initialCapacity = MAXIMUM_CAPACITY;
        if (loadFactor <= 0 || Float.isNaN(loadFactor))
            throw new IllegalArgumentException("Illegal load factor: " +
                                               loadFactor);
        this.loadFactor = loadFactor;
        this.threshold = tableSizeFor(initialCapacity);
    }
    步驟2：添加方法 下面這個方法是調(diào)用了 LinkedHashMap的父類HashMap中的put方法
    public boolean add(E e) {
        return map.put(e, PRESENT)==null;
    }
    調(diào)用 HashMap 中 put 方法
    public V put(K key, V value) {
        return putVal(hash(key), key, value, false, true);
    }
    繼承調(diào)用 HashMap方法中 putVal 方法
    final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                   boolean evict) {
        Node<K,V>[] tab; Node<K,V> p; int n, i;
        如果 table 表為null并且長度為0時，則調(diào)用 resize 方法完成擴容
        if ((tab = table) == null || (n = tab.length) == 0)
            n = (tab = resize()).length;
        if ((p = tab[i = (n - 1) & hash]) == null)
            tab[i] = newNode(hash, key, value, null);
        else {
            Node<K,V> e; K k;
            if (p.hash == hash &&
                ((k = p.key) == key || (key != null && key.equals(k))))
                e = p;
            else if (p instanceof TreeNode)
                e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
            else {
                for (int binCount = 0; ; ++binCount) {
                    if ((e = p.next) == null) {
                        p.next = newNode(hash, key, value, null);
                        if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                            treeifyBin(tab, hash);
                        break;
                    }
                    if (e.hash == hash &&
                        ((k = e.key) == key || (key != null && key.equals(k))))
                        break;
                    p = e;
                }
            }
            if (e != null) { // existing mapping for key
                V oldValue = e.value;
                if (!onlyIfAbsent || oldValue == null)
                    e.value = value;
                afterNodeAccess(e);
                return oldValue;
            }
        }
        ++modCount;
        if (++size > threshold)
            resize();
        afterNodeInsertion(evict);
        return null;
    }
    在創(chuàng)建 newNode 節(jié)點會動態(tài)綁定到 LinkedHashMap 中的 newNode 方法
    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); 完成雙向鏈表之間的連接
        return p;
    }
    再調(diào)用 LinkedHashMap 中的靜態(tài)內(nèi)部類
    static class Entry<K,V> extends HashMap.Node<K,V> {
        Entry<K,V> before, after;
        Entry(int hash, K key, V value, Node<K,V> next) {
            super(hash, key, value, next);
        }
    }
    繼續(xù)調(diào)用本類 靜態(tài)內(nèi)部類 Node 完成屬性的初始化
    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;
        }
    最后調(diào)用本類 LinkedHashMap類中 linkNodeLat 方法完成前后的指向形成鏈表
     private void linkNodeLast(LinkedHashMap.Entry<K,V> p) {
        LinkedHashMap.Entry<K,V> last = tail;
        tail = p;
        if (last == null)
            head = p;
        else {
            p.before = last;
            last.after = p;
        }
      }