static class Entry<K,V> implements Map.Entry<K,V> {
    final K key;
    V value;
    Entry<K,V> next;
    int hash;

    /**
     * Creates new entry.
     */
    Entry(int h, K k, V v, Entry<K,V> n) {
      value = v;
      next = n;
      key = k;
      hash = h;
    }

    public final K getKey() {
      return key;
    }

    public final V getValue() {
      return value;
    }

    public final V setValue(V newValue) {
      V oldValue = value;
      value = newValue;
      return oldValue;
    }

    public final boolean equals(Object o) {
      if (!(o instanceof Map.Entry))
        return false;
      Map.Entry e = (Map.Entry)o;
      Object k1 = getKey();
      Object k2 = e.getKey();
      if (k1 == k2 || (k1 != null && k1.equals(k2))) {
        Object v1 = getValue();
        Object v2 = e.getValue();
        if (v1 == v2 || (v1 != null && v1.equals(v2)))
          return true;
      }
      return false;
    }

    public final int hashCode() {
      return Objects.hashCode(getKey()) ^ Objects.hashCode(getValue());
    }

    public final String toString() {
      return getKey() + "=" + getValue();
    }

    /**
     * This method is invoked whenever the value in an entry is
     * overwritten by an invocation of put(k,v) for a key k that's already
     * in the HashMap.
     */
    void recordAccess(HashMap<K,V> m) {
    }

    /**
     * This method is invoked whenever the entry is
     * removed from the table.
     */
    void recordRemoval(HashMap<K,V> m) {
    }
  }

public V put(K key, V value) {
    if (table == EMPTY_TABLE) {
      inflateTable(threshold);
    }
    if (key == null)
      return putForNullKey(value);

　　　　　//以上信息不关心，下面是正常的插入逻辑。

　　　　　//首先计算hashCode
    int hash = hash(key);
　　　　　//通过计算得到的hashCode，计算出hashCode在数组中的位置
    int i = indexFor(hash, table.length);

　　　　　//for循环，找到在HashMap中是否存在一个节点，对应的key与传入的key完全一致。如果存在，说明用户想要替换该key对应的value值，因此直接替换value即可返回。
    for (Entry<K,V> e = table[i]; e != null; e = e.next) {
      Object k;
      if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
        V oldValue = e.value;
        e.value = value;
        e.recordAccess(this);
        return oldValue;
      }
    }

　　　　 //逻辑执行到此处，说明HashMap中不存在完全一致的kye.调用addEntry，新建一个节点保存key、value信息，并增加到HashMap中
    modCount++;
    addEntry(hash, key, value, i);
    return null;
  }

　static int indexFor(int h, int length) {
    // assert Integer.bitCount(length) == 1 : "length must be a non-zero power of 2";
    return h & (length-1);
  }

private void inflateTable(int toSize) {
// Find a power of 2 >= toSize
int capacity = roundUpToPowerOf2(toSize);

threshold = (int) Math.min(capacity * loadFactor, MAXIMUM_CAPACITY + 1);
table = new Entry[capacity];
initHashSeedAsNeeded(capacity);
}

/**
   * Adds a new entry with the specified key, value and hash code to
   * the specified bucket. It is the responsibility of this
   * method to resize the table if appropriate.
   *
   * Subclass overrides this to alter the behavior of put method.
   */
  void addEntry(int hash, K key, V value, int bucketIndex) {
    if ((size >= threshold) && (null != table[bucketIndex])) {
      resize(2 * table.length);
      hash = (null != key) ? hash(key) : 0;
      bucketIndex = indexFor(hash, table.length);
    }

    createEntry(hash, key, value, bucketIndex);
  }

  /**
   * Like addEntry except that this version is used when creating entries
   * as part of Map construction or "pseudo-construction" (cloning,
   * deserialization). This version needn't worry about resizing the table.
   *
   * Subclass overrides this to alter the behavior of HashMap(Map),
   * clone, and readObject.
   */
  void createEntry(int hash, K key, V value, int bucketIndex) {
    Entry<K,V> e = table[bucketIndex];
    table[bucketIndex] = new Entry<>(hash, key, value, e);
    size++;
  }

 private static class Entry<K,V> extends HashMap.Entry<K,V> {
    // These fields comprise the doubly linked list used for iteration.
    Entry<K,V> before, after;

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

    /**
     * Removes this entry from the linked list.
     */
    private void remove() {
      before.after = after;
      after.before = before;
    }

    /**
     * Inserts this entry before the specified existing entry in the list.
     */
    private void addBefore(Entry<K,V> existingEntry) {
      after = existingEntry;
      before = existingEntry.before;
      before.after = this;
      after.before = this;
    }

    /**
     * This method is invoked by the superclass whenever the value
     * of a pre-existing entry is read by Map.get or modified by Map.set.
     * If the enclosing Map is access-ordered, it moves the entry
     * to the end of the list; otherwise, it does nothing.
     */
    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();
    }
  }

 /**
   * This override alters behavior of superclass put method. It causes newly
   * allocated entry to get inserted at the end of the linked list and
   * removes the eldest entry if appropriate.
   */
  void addEntry(int hash, K key, V value, int bucketIndex) {
    super.addEntry(hash, key, value, bucketIndex);

    // Remove eldest entry if instructed
    Entry<K,V> eldest = header.after;
    if (removeEldestEntry(eldest)) {
      removeEntryForKey(eldest.key);
    }
  }

  /**
   * This override differs from addEntry in that it doesn't resize the
   * table or remove the eldest entry.
   */
  void createEntry(int hash, K key, V value, int bucketIndex) {
    HashMap.Entry<K,V> old = table[bucketIndex];
    Entry<K,V> e = new Entry<>(hash, key, value, old);
    table[bucketIndex] = e;
    e.addBefore(header);
    size++;
  }

　void addEntry(int hash, K key, V value, int bucketIndex) {
    if ((size >= threshold) && (null != table[bucketIndex])) {
      resize(2 * table.length);
      hash = (null != key) ? hash(key) : 0;
      bucketIndex = indexFor(hash, table.length);
    }

    HashMap.Entry<K,V> old = table[bucketIndex];
    Entry<K,V> e = new Entry<>(hash, key, value, old);
    table[bucketIndex] = e;
    e.addBefore(header);
    size++;

    // Remove eldest entry if instructed
    Entry<K,V> eldest = header.after;
    if (removeEldestEntry(eldest)) {
      removeEntryForKey(eldest.key);
    }
  }

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

  // Remove eldest entry if instructed
    Entry<K,V> eldest = header.after;
    if (removeEldestEntry(eldest)) {
      removeEntryForKey(eldest.key);
    }

　final Entry<K,V> removeEntryForKey(Object key) {
    if (size == 0) {
      return null;
    }
    int hash = (key == null) ? 0 : hash(key);
    int i = indexFor(hash, table.length);
    Entry<K,V> prev = table[i];
    Entry<K,V> e = prev;

    while (e != null) {
      Entry<K,V> next = e.next;
      Object k;
      if (e.hash == hash &&
        ((k = e.key) == key || (key != null && key.equals(k)))) {
        modCount++;
        size--;
        if (prev == e)
          table[i] = next;
        else
          prev.next = next;
        e.recordRemoval(this);
        return e;
      }
      prev = e;
      e = next;
    }

    return e;
  }

 /**
     * Removes this entry from the linked list.
     */
    private void remove() {
      before.after = after;
      after.before = before;
    }void recordRemoval(HashMap<K,V> m) {
      remove();
    }

public V get(Object key) {
    Entry<K,V> e = (Entry<K,V>)getEntry(key);
    if (e == null)
      return null;
    e.recordAccess(this);
    return e.value;
  }

　　 /**
     * Removes this entry from the linked list.
     */
    private void remove() {
      before.after = after;
      after.before = before;
    }

    /**
     * Inserts this entry before the specified existing entry in the list.
     */
    private void addBefore(Entry<K,V> existingEntry) {
      after = existingEntry;
      before = existingEntry.before;
      before.after = this;
      after.before = this;
    }

    /**
     * This method is invoked by the superclass whenever the value
     * of a pre-existing entry is read by Map.get or modified by Map.set.
     * If the enclosing Map is access-ordered, it moves the entry
     * to the end of the list; otherwise, it does nothing.
     */
    void recordAccess(HashMap<K,V> m) {
      LinkedHashMap<K,V> lm = (LinkedHashMap<K,V>)m;
      if (lm.accessOrder) {
        lm.modCount++;
        remove();
        addBefore(lm.header);
      }
    }

　public void trimToSize(int maxSize)
 {
  while (true)
  {
   Object key;
   Object value;
   synchronized (this) {
    if ((this.size < 0) || ((this.map.isEmpty()) && (this.size != 0))) {
     throw new IllegalStateException(getClass().getName() + ".sizeOf() is reporting inconsistent results!");
    }
　　　　　　if (size <= maxSize) {
　　　　　　　　break;
　　　　　　}

    Map.Entry toEvict = (Map.Entry)this.map.entrySet().iterator().next();

    key = toEvict.getKey();
    value = toEvict.getValue();
    this.map.remove(key);
    this.size -= safeSizeOf(key, value);
    this.evictionCount += 1;
   }

   entryRemoved(true, key, value, null);
  }
 }

public Set<Entry<K, V>> entrySet() {
    Set<Entry<K, V>> es = entrySet;
    return (es != null) ? es : (entrySet = new EntrySet());
  }

private final class EntrySet extends AbstractSet<Entry<K, V>> {
    public Iterator<Entry<K, V>> iterator() {
      return newEntryIterator();
    }
    public boolean contains(Object o) {
      if (!(o instanceof Entry))
        return false;
      Entry<?, ?> e = (Entry<?, ?>) o;
      return containsMapping(e.getKey(), e.getValue());
    }
    public boolean remove(Object o) {
      if (!(o instanceof Entry))
        return false;
      Entry<?, ?> e = (Entry<?, ?>)o;
      return removeMapping(e.getKey(), e.getValue());
    }
    public int size() {
      return size;
    }
    public boolean isEmpty() {
      return size == 0;
    }
    public void clear() {
      HashMap.this.clear();
    }
  }

　　Iterator<Entry<K, V>> newEntryIterator() { return new EntryIterator(); }

　　private final class EntryIterator
      extends LinkedHashIterator<Map.Entry<K, V>> {
    public final Map.Entry<K, V> next() { return nextEntry(); }
  }

  private abstract class LinkedHashIterator<T> implements Iterator<T> {
    LinkedEntry<K, V> next = header.nxt;
    LinkedEntry<K, V> lastReturned = null;
    int expectedModCount = modCount;

    public final boolean hasNext() {
      return next != header;
    }

    final LinkedEntry<K, V> nextEntry() {
      if (modCount != expectedModCount)
        throw new ConcurrentModificationException();
      LinkedEntry<K, V> e = next;
      if (e == header)
        throw new NoSuchElementException();
      next = e.nxt;
      return lastReturned = e;
    }

    public final void remove() {
      if (modCount != expectedModCount)
        throw new ConcurrentModificationException();
      if (lastReturned == null)
        throw new IllegalStateException();
      LinkedHashMap.this.remove(lastReturned.key);
      lastReturned = null;
      expectedModCount = modCount;
    }
  }