分析HashMap 的 JDK 源码

Map map = new HashMap();
  
map.put(1, "张三");
map.put(2, "李四");
map.put(3, "王五");
map.put(4, "赵六");
map.put(5, "钱七");
  
Set set = map.entrySet();
for (Object object : set) {
  Map.Entry entry = (Map.Entry) object;
  System.out.println(entry.getKey() + "-->" + entry.getValue());
}

final class EntrySet extends AbstractSet<Map.Entry<K,V>> {
  public final int size() {
    return size;
  }

  public final void clear() {
    HashMap.this.clear();
  }

  public final Iterator<Map.Entry<K,V>> iterator() {
    return new EntryIterator();
  }

  public final boolean contains(Object o) {
    if (!(o instanceof Map.Entry))
      return false;
    Map.Entry<?,?> e = (Map.Entry<?,?>) o;
    Object key = e.getKey();
    Node<K,V> candidate = getNode(hash(key), key);
    return candidate != null && candidate.equals(e);
  }

  public final boolean remove(Object o) {
    if (o instanceof Map.Entry) {
      Map.Entry<?,?> e = (Map.Entry<?,?>) o;
      Object key = e.getKey();
      Object value = e.getValue();
      return removeNode(hash(key), key, value, true, true) != null;
    }
    return false;
  }

  public final Spliterator<Map.Entry<K,V>> spliterator() {
    return new EntrySpliterator<>(HashMap.this, 0, -1, 0, 0);
  }

  public final void forEach(Consumer<? super Map.Entry<K,V>> action) {
    Node<K,V>[] tab;
    if (action == null)
      throw new NullPointerException();
    if (size > 0 && (tab = table) != null) {
      int mc = modCount;
      for (int i = 0; i < tab.length; ++i) {
        for (Node<K,V> e = tab[i]; e != null; e = e.next)
          action.accept(e);
      }
      if (modCount != mc)
        throw new ConcurrentModificationException();
    }
  }
}

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 final K getKey() {
    return key;
  }

  public final V getValue() {
    return value;
  }

  public final String toString() {
    return key + "=" + value;
  }

  public final int hashCode() {
    return Objects.hashCode(key) ^ Objects.hashCode(value);
  }

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

  public final boolean equals(Object o) {
    if (o == this)
      return true;
    if (o instanceof Map.Entry) {
      Map.Entry<?,?> e = (Map.Entry<?,?>)o;
      if (Objects.equals(key, e.getKey()) &&
        Objects.equals(value, e.getValue()))
        return true;
    }
    return false;
  }
}