/** 
 * 雙向鏈表的表頭元素。 
 */  
private transient Entry<K,V> header;  
/** 
 * LinkedHashMap的Entry元素。 
 * 繼承HashMap的Entry元素，又保存了其上一個(gè)元素before和下一個(gè)元素after的引用。 
 */  
private static class Entry<K,V> extends HashMap.Entry<K,V> {  
    Entry<K,V> before, after;  
    ……  
}  

public LinkedHashMap(int initialCapacity, float loadFactor) {  
    super(initialCapacity, loadFactor);  
    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);  
    // Find a power of 2 >= initialCapacity  
    int capacity = 1;  
    while (capacity < initialCapacity)  
        capacity <<= 1;  
    this.loadFactor = loadFactor;  
    threshold = (int)(capacity * loadFactor);  
    table = new Entry[capacity];  
    init();  
}  

void init() {  
    header = new Entry<K,V>(-1, null, null, null);  
    header.before = header.after = header;  
}  

void addEntry(int hash, K key, V value, int bucketIndex) {  
    // 調(diào)用create方法，將新元素以雙向鏈表的的形式加入到映射中。  
    createEntry(hash, key, value, bucketIndex);  
    // 刪除最近最少使用元素的策略定義  
    Entry<K,V> eldest = header.after;  
    if (removeEldestEntry(eldest)) {  
        removeEntryForKey(eldest.key);  
    } else {  
        if (size >= threshold)  
            resize(2 * table.length);  
    }  
}  

void createEntry(int hash, K key, V value, int bucketIndex) {  
    HashMap.Entry<K,V> old = table[bucketIndex];  
    Entry<K,V> e = new Entry<K,V>(hash, key, value, old);  
    table[bucketIndex] = e;  
    // 調(diào)用元素的addBrefore方法，將元素加入到哈希、雙向鏈接列表。  
    e.addBefore(header);  
    size++;  
}  

private void addBefore(Entry<K,V> existingEntry) {  
    after  = existingEntry;  
    before = existingEntry.before;  
    before.after = this;  
    after.before = this;  
}  

public V get(Object key) {  
    // 調(diào)用父類(lèi)HashMap的getEntry()方法，取得要查找的元素。  
    Entry<K,V> e = (Entry<K,V>)getEntry(key);  
    if (e == null)  
        return null;  
    // 記錄訪問(wèn)順序。  
    e.recordAccess(this);  
    return e.value;  
}  

void recordAccess(HashMap<K,V> m) {  
    LinkedHashMap<K,V> lm = (LinkedHashMap<K,V>)m;  
    // 如果定義了LinkedHashMap的迭代順序?yàn)樵L問(wèn)順序，  
    // 則刪除以前位置上的元素，并將最新訪問(wèn)的元素添加到鏈表表頭。  
    if (lm.accessOrder) {  
        lm.modCount++;  
        remove();  
        addBefore(lm.header);  
    }  
}  

private final boolean accessOrder;  

public LinkedHashMap(int initialCapacity, float loadFactor) {  
    super(initialCapacity, loadFactor);  
    accessOrder = false;  
}  

public LinkedHashMap(int initialCapacity,  
         float loadFactor,  
                     boolean accessOrder) {  
    super(initialCapacity, loadFactor);  
    this.accessOrder = accessOrder;  
}  

protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {  
    return false;  
}  

private static final int MAX_ENTRIES = 100;  
protected boolean removeEldestEntry(Map.Entry eldest) {  
    return size() > MAX_ENTRIES;  
}