JDK容器学习之TreeMap (一) : 底层数据结构

public class TreeMap<K,V>
    extends AbstractMap<K,V>
    implements NavigableMap<K,V>, Cloneable, java.io.Serializable {
  // ....    
}

// 既然叫做SortMap, 要排序的话，当然需要一个比较器了
Comparator<? super K> comparator();

SortedMap<K,V> subMap(K fromKey, K toKey);

// 源码注释: 返回比Map中key比参数toKey小的所有kv对
SortedMap<K,V> headMap(K toKey);

// 源码注释：返回比Map中key比参数fromKey大或相等的所有kv对
SortedMap<K,V> tailMap(K fromKey);

K firstKey();

K lastKey();

// 返回Map中比传入参数key小的kv对中，key最大的一个kv对
Map.Entry<K,V> lowerEntry(K key);
K lowerKey(K key);

// 返回Map中比传入参数key小或相等的kv对中，key最大的一个kv对
Map.Entry<K,V> floorEntry(K key);
K floorKey(K key);

// 返回Map中比传入参数key大或相等的kv对中，key最小的一个kv对
Map.Entry<K,V> ceilingEntry(K key);
K ceilingKey(K key);

// 返回Map中比传入参数key大的kv对中，key最小的一个kv对
Map.Entry<K,V> higherEntry(K key);
K higherKey(K key);


Map.Entry<K,V> firstEntry();
Map.Entry<K,V> lastEntry();
Map.Entry<K,V> pollFirstEntry();
NavigableMap<K,V> descendingMap();
NavigableSet<K> navigableKeySet();
NavigableSet<K> descendingKeySet();

private transient Entry<K,V> root;

static final class Entry<K,V> implements Map.Entry<K,V> {
  K key;
  V value;
  Entry<K,V> left;
  Entry<K,V> right;
  Entry<K,V> parent;
  boolean color = BLACK;

  /**
   * Make a new cell with given key, value, and parent, and with
   * {@code null} child links, and BLACK color.
   */
  Entry(K key, V value, Entry<K,V> parent) {
      this.key = key;
      this.value = value;
      this.parent = parent;
  }

  /**
   * Returns the key.
   *
   * @return the key
   */
  public K getKey() {
      return key;
  }

  /**
   * Returns the value associated with the key.
   *
   * @return the value associated with the key
   */
  public V getValue() {
      return value;
  }

  /**
   * Replaces the value currently associated with the key with the given
   * value.
   *
   * @return the value associated with the key before this method was
   *         called
   */
  public V setValue(V value) {
      V oldValue = this.value;
      this.value = value;
      return oldValue;
  }

  public boolean equals(Object o) {
      if (!(o instanceof Map.Entry))
          return false;
      Map.Entry<?,?> e = (Map.Entry<?,?>)o;

      return valEquals(key,e.getKey()) && valEquals(value,e.getValue());
  }

  public int hashCode() {
      int keyHash = (key==null ? 0 : key.hashCode());
      int valueHash = (value==null ? 0 : value.hashCode());
      return keyHash ^ valueHash;
  }

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

public V put(K key, V value) {
  Entry<K,V> t = root;
  if (t == null) {
      // 奇怪的一行逻辑，感觉并没有什么用
      compare(key, key); // type (and possibly null) check

      root = new Entry<>(key, value, null);
      size = 1;
      modCount++;
      return null;
  }
  int cmp;
  Entry<K,V> parent;
  // split comparator and comparable paths
  Comparator<? super K> cpr = comparator;
  if (cpr != null) {
      // 下面这个循环可以得出树的左节点小于根小于右节点
      // 然后找到新增的节点，作为叶子节点在树中的位置
      // 注意这个相等时，直接更新了value值（这里表示插入一条已存在的记录）
      do {
          parent = t;
          cmp = cpr.compare(key, t.key);
          if (cmp < 0)
              t = t.left;
          else if (cmp > 0)
              t = t.right;
          else
              return t.setValue(value);
      } while (t != null);
  }
  else { 
      // 比较器不存在的逻辑，这时要求key继承 Comparable 接口
      if (key == null)
          throw new NullPointerException();
      @SuppressWarnings("unchecked")
          Comparable<? super K> k = (Comparable<? super K>) key;
      do {
          parent = t;
          cmp = k.compareTo(t.key);
          if (cmp < 0)
              t = t.left;
          else if (cmp > 0)
              t = t.right;
          else
              return t.setValue(value);
      } while (t != null);
  }
  
  // 创建一个Entry节点
  Entry<K,V> e = new Entry<>(key, value, parent);
  if (cmp < 0)
      parent.left = e;
  else
      parent.right = e;
      
  // 红黑树的重排
  fixAfterInsertion(e);
  size++;
  modCount++;
  return null;
}