Java--TreeMap源码解读

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TreeMap

public class TreeMap<K,V> extends AbstractMap<K,V>
 implements NavigableMap<K,V>, Cloneable, Serializable
   TreeMap基于红黑树（Red-Black tree）实现，根据键值的自然顺序进行排序，或者根据创建映射时提供的Comparator进行排序。此实现为 containsKey、get、put 和 remove 操作提供受保证的 log(n) 时间开销。
     是线程不安全的，同样会触发fail-fast，抛出ConcurrentModificationException。
final Entry<K,V> getEntry(Object key) {        // Offload comparator-based version for sake of performance        if (comparator != null)            return getEntryUsingComparator(key);        if (key == null)            throw new NullPointerException();Comparable<? super K> k = (Comparable<? super K>) key;        Entry<K,V> 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;    }
因为TreeMap是已经排好序的，所以当查询某个值时，根据相应的comparator来比较，是去其左子树查找还是去右子树查找。

 public V put(K key, V value) {        Entry<K,V> t = root;        if (t == null) {    // TBD:    // 5045147: (coll) Adding null to an empty TreeSet should    // throw NullPointerException    //    // compare(key, key); // type check            root = new Entry<K,V>(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) {            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 {            if (key == null)                throw new NullPointerException();            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);        }        Entry<K,V> e = new Entry<K,V>(key, value, parent);        if (cmp < 0)            parent.left = e;        else            parent.right = e;        fixAfterInsertion(e);        size++;        modCount++;        return null;    }
put（）方法根据是否有自己设定的comparator，分为两种方式进行插值。

private void deleteEntry(Entry<K,V> p) {        modCount++;        size--;        // If strictly internal, copy successor's element to p and then make p        // point to successor.        if (p.left != null && p.right != null) {            Entry<K,V> s = successor (p);            p.key = s.key;            p.value = s.value;            p = s;        } // p has 2 children        // Start fixup at replacement node, if it exists.        Entry<K,V> replacement = (p.left != null ? p.left : p.right);        if (replacement != null) {            // Link replacement to parent            replacement.parent = p.parent;            if (p.parent == null)                root = replacement;            else if (p == p.parent.left)                p.parent.left  = replacement;            else                p.parent.right = replacement;            // Null out links so they are OK to use by fixAfterDeletion.            p.left = p.right = p.parent = null;            // Fix replacement            if (p.color == BLACK)                fixAfterDeletion(replacement);        } else if (p.parent == null) { // return if we are the only node.            root = null;        } else { //  No children. Use self as phantom replacement and unlink.            if (p.color == BLACK)                fixAfterDeletion(p);            if (p.parent != null) {                if (p == p.parent.left)                    p.parent.left = null;                else if (p == p.parent.right)                    p.parent.right = null;                p.parent = null;            }        }    }

remove（）方法，移除某个值。

基于红黑树在插入和删除后进行调整。
 private void fixAfterInsertion(Entry<K,V> x) {        x.color = RED;        while (x != null && x != root && x.parent.color == RED) {            if (parentOf(x) == leftOf(parentOf(parentOf(x)))) {                Entry<K,V> y = rightOf(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 == rightOf(parentOf(x))) {                        x = parentOf(x);                        rotateLeft(x);                    }                    setColor(parentOf(x), BLACK);                    setColor(parentOf(parentOf(x)), RED);                    rotateRight(parentOf(parentOf(x)));                }            } else {                Entry<K,V> 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;    }


private void fixAfterDeletion(Entry<K,V> x) {        while (x != root && colorOf(x) == BLACK) {            if (x == leftOf(parentOf(x))) {                Entry<K,V> sib = rightOf(parentOf(x));                if (colorOf(sib) == RED) {                    setColor(sib, BLACK);                    setColor(parentOf(x), RED);                    rotateLeft(parentOf(x));                    sib = rightOf(parentOf(x));                }                if (colorOf(leftOf(sib))  == BLACK &&                    colorOf(rightOf(sib)) == BLACK) {                    setColor(sib, RED);                    x = parentOf(x);                } else {                    if (colorOf(rightOf(sib)) == BLACK) {                        setColor(leftOf(sib), BLACK);                        setColor(sib, RED);                        rotateRight(sib);                        sib = rightOf(parentOf(x));                    }                    setColor(sib, colorOf(parentOf(x)));                    setColor(parentOf(x), BLACK);                    setColor(rightOf(sib), BLACK);                    rotateLeft(parentOf(x));                    x = root;                }            } else { // symmetric                Entry<K,V> sib = leftOf(parentOf(x));                if (colorOf(sib) == RED) {                    setColor(sib, BLACK);                    setColor(parentOf(x), RED);                    rotateRight(parentOf(x));                    sib = leftOf(parentOf(x));                }                if (colorOf(rightOf(sib)) == BLACK &&                    colorOf(leftOf(sib)) == BLACK) {                    setColor(sib, RED);                    x = parentOf(x);                } else {                    if (colorOf(leftOf(sib)) == BLACK) {                        setColor(rightOf(sib), BLACK);                        setColor(sib, RED);                        rotateLeft(sib);                        sib = leftOf(parentOf(x));                    }                    setColor(sib, colorOf(parentOf(x)));                    setColor(parentOf(x), BLACK);                    setColor(leftOf(sib), BLACK);                    rotateRight(parentOf(x));                    x = root;                }            }        }        setColor(x, BLACK);    }


其详细的操作步骤可以看红黑树的详细内容。

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