三、TreeMap和TreeSet

所有集合基于jdk1.8，对源码稍做调整。

HashMap

主要变量

    // 比较器
    private final Comparator comparator;
    // 根节点
    private transient Entry root;
    // TreeMap大小
    private transient int size = 0;
    // 修改量
    private transient int modCount = 0;

构造方法

    TreeMap() {
        this.comparator = null;
    }

    TreeMap(Comparator comparator) {
        this.comparator = comparator;
    }

    public TreeMap(Map m) {
        comparator = null;
        putAll(m);
    }

    public TreeMap(SortedMap m) {
        comparator = m.comparator();
        try {
            buildFromSorted(m.size(), m.entrySet().iterator(), null, null);
        } catch (java.io.IOException cannotHappen) {
        } catch (ClassNotFoundException cannotHappen) {
        }
    }
    

put

    public V put(K key, V value) {
        Entry t = root;
        //当根节点为空，直接赋值给根节点
        if (t == null) {
            compare(key, key);

            root = new Entry<>(key, value, null);
            size = 1;
            modCount++;
            return null;
        }
        int cmp;
        Entry parent;

        Comparator cpr = comparator;
        //比较器存在时，按照比较器进行比较
        if (cpr != null) {
            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);
        }
        //比较器不存在，调用key的compare方法
        else {
            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;
                else if (cmp > 0)
                    t = t.right;
                else
                    return t.setValue(value);
            } while (t != null);
        }
        Entry e = new Entry<>(key, value, parent);
        if (cmp < 0)
            parent.left = e;
        else
            parent.right = e;
        //红黑树实现
        fixAfterInsertion(e);
        size++;
        modCount++;
        return null;
    }

    /**
     * 红黑树实现
     * @param x
     */
    private void fixAfterInsertion(Entry x) {
        //先设为红色节点
        x.color = RED;
        //父颜色P为红时，进行变换（红黑树不允许分支上连续出现红色节点）
        while (x != null && x != root && x.parent.color == RED) {
            //当P在其父节点G左边时
            if (parentOf(x) == leftOf(parentOf(parentOf(x)))) {
                //获取G的右子树Y
                Entry y = rightOf(parentOf(parentOf(x)));
                //Y为红,设P为红，Y为黑，G为红,G变换为X继续迭代
                if (colorOf(y) == RED) {
                    setColor(parentOf(x), BLACK);
                    setColor(y, BLACK);
                    setColor(parentOf(parentOf(x)), RED);
                    x = parentOf(parentOf(x));
                } 
                //Y为黑
                else {
                    //X在右边时，X转换为父节点并进行左旋
                    if (x == rightOf(parentOf(x))) {
                        x = parentOf(x);
                        rotateLeft(x);
                    }
                    //将X父节点设为黑色，父节点的父节点G设为红色，并将G右旋
                    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;
    }

get

    public V get(Object key) {
        Entry p = getEntry(key);
        return (p == null ? null : p.value);
    }

    final Entry getEntry(Object key) {
        if (comparator != null)
            return getEntryUsingComparator(key);
        if (key == null)
            throw new NullPointerException();
        @SuppressWarnings("unchecked")
        Comparable k = (Comparable) key;
        Entry p = root;
        while (p != null) {
            int cmp = k.compareTo(p.key);
            if (cmp < 0)
                p = p.left;
            else if (cmp > 0)
                p = p.right;
            else
                return p;
        }
        return null;
    }

TreeSet

TreeSet内部维护了一个TreeMap，元素不重复也是依靠TreeMap的key值不重复实现的。

主要变量

    //实际元素
    private transient NavigableMap m;
    //充当每个key的对应value
    private static final Object PRESENT = new Object();