TreeMap源码分析

/**

• The comparator used to maintain order in this tree map, or
• null if it uses the natural ordering of its keys.

• @serial
  */
  //自然排序
  private final Comparator comparator;
  //根节点
  private transient Entry root;

  /**

• The number of entries in the tree
  */
  //大小
  private transient int size = 0;

public TreeMap() {
comparator = null;
}

public V put(K key, V value) {
Entry t = root;//红黑树的根节点
if (t == null) {
compare(key, key); // type (and possibly null) check

        root = new Entry<>(key, value, null);//构造根节点，root没有父节点，传入null
        size = 1;
        modCount++;
        return null;
    }
    int cmp;
    Entry parent;  //定义节点
    // split comparator and comparable paths
    Comparator cpr = comparator; //获得比较器
    if (cpr != null) {//定义了比较器，采用自定义比较器进行比较
        do {
            parent = t;//将红黑树根节点赋值给parent
            cmp = cpr.compare(key, t.key);
            if (cmp < 0)
                t = t.left;//指向左子节点
            else if (cmp > 0)
                t = t.right;//指向右子节点
            else
                return t.setValue(value);
        } while (t != null);
    }
    else {
        //自然排序，没有指定比较器
        if (key == null)
            throw new NullPointerException();
        @SuppressWarnings("unchecked")
            Comparable k = (Comparable) key;
        do {
            parent = t;
            cmp = k.compareTo(t.key);
            if (cmp < 0)
                t = t.left;//左子节点
            else if (cmp > 0)
                t = t.right;//右子节点
            else
                return t.setValue(value);
        } while (t != null);
    }
    //创建新节点，并指定父点
    Entry e = new Entry<>(key, value, parent);
    if (cmp < 0)
        parent.left = e;
    else
        parent.right = e;
    //新插入节点后重新调整红黑树
    fixAfterInsertion(e);
    size++;
    modCount++;
    return null;
}

/** From CLR */
private void fixAfterInsertion(Entry x) {
    //加入的节点默认的颜色是红色
    x.color = RED;
    //情形1：新节点x是树的根节点，没有父节点不需要任何操作
    //情形2：新节点x的父节点颜色是黑色的，不需要操作
    while (x != null && x != root && x.parent.color == RED) {
        //情形3：新节点的父节点颜色是红色的
        //判断x的节点的父节点位置，是否属于左子节点
        if (parentOf(x) == leftOf(parentOf(parentOf(x)))) {
            //获取x节点的父节点的兄弟节点，上面语句已经判断出x节点的父节点为左子节点，所以直接取右子节点
            Entry y = rightOf(parentOf(parentOf(x)));
            //判断是否x节点的父节点的兄弟节点为红色
            if (colorOf(y) == RED) {
                setColor(parentOf(x), BLACK);//x节点的父节点设置为黑色
                setColor(y, BLACK);//y节点的颜色设置为黑色
                setColor(parentOf(parentOf(x)), RED);//x的父节点的父节点设置为红色
                x = parentOf(parentOf(x));
            } else {
                if (x == rightOf(parentOf(x))) {
                    x = parentOf(x);
                    rotateLeft(x);
                }
                setColor(parentOf(x), BLACK);
                setColor(parentOf(parentOf(x)), RED);
                rotateRight(parentOf(parentOf(x)));
            }
        } else {
            Entry y = leftOf(parentOf(parentOf(x)));
            if (colorOf(y) == RED) {
                setColor(parentOf(x), BLACK);
                setColor(y, BLACK);
                setColor(parentOf(parentOf(x)), RED);
                x = parentOf(parentOf(x));
            } else {
                if (x == leftOf(parentOf(x))) {
                    x = parentOf(x);
                    rotateRight(x);
                }
                setColor(parentOf(x), BLACK);
                setColor(parentOf(parentOf(x)), RED);
                rotateLeft(parentOf(parentOf(x)));
            }
        }
    }
    root.color = BLACK;
}