原文链 id="treemap详解">TreeMap详解
TreeMap是Map接口的一个实现类，底层基于红黑树的实现
从继承机构可以看到TreeMap除了继承了AbstractMap类，还实现了NavigableMap接口，而NavigableMap接口是继承自SortedMap接口的，所以TreeMap是可以进行排序的
关键变量
// 比较器，根据比较器来决定TreeMap的排序，如果为空，按照key做自然排序(最小的在根节点)private final Comparator<? super K> comparator;// 根节点private transient Entry<K,V> root;/** * The number of entries in the tree * 树的大小 */private transient int size = 0;/** * The number of structural modifications to the tree. * 修改次数 */private transient int modCount = 0;// Entry为TreeMap的内部类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;}构造函数
// 默认空参构造器，比较器设置为空public TreeMap() { comparator = null;}// 提供比较器public TreeMap(Comparator<? super K> comparator) { this.comparator = comparator;}public TreeMap(Map<? extends K, ? extends V> m) { comparator = null; putAll(m);}public TreeMap(SortedMap<K, ? extends V> m) { comparator = m.comparator(); try { buildFromSorted(m.size(), m.entrySet().iterator(), null, null); } catch (java.io.IOException cannotHappen) { } catch (ClassNotFoundException cannotHappen) { }}get方法
public V get(Object key) { Entry<K,V> p = getEntry(key); return (p==null ? null : p.value);}final Entry<K,V> getEntry(Object key) { // Offload comparator-based version for sake of performance if (comparator != null) return getEntryUsingComparator(key); // 从这里可以看出TreeMap的key不可以为null if (key == null) throw new NullPointerException(); @SuppressWarnings("unchecked") Comparable<? super K> k = (Comparable<? super K>) key; // 获取根节点 Entry<K,V> p = root; while (p != null) { // 判断是根节点的左子树还是右子树 int cmp = k.compareTo(p.key); if (cmp < 0) p = p.left; else if (cmp > 0) p = p.right; else return p; } return null;}put方法
public V put(K key, V value) { Entry<K,V> t = root; // 根节点为null，表示这是第一个元素 if (t == null) { // 主要是为了确保key是可排序的类，以及key不能为null compare(key, key); // type (and possibly null) check // 第三个参数为父节点的entry，根节点没有父节点，所以为null 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; // 存在比较器的情况 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); } // 不存在比较器，进行自然排序 else { // key不能为null if (key == null) throw new NullPointerException(); @SuppressWarnings("unchecked") Comparable<? super K> k = (Comparable<? super K>) key; // do...while是为了找到该key所要存放的位置(找到父节点) 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<>(key, value, parent); // 比父节点小，是左子树 if (cmp < 0) parent.left = e; else parent.right = e; // 插入之后还要进行平衡操作 fixAfterInsertion(e); size++; modCount++; return null;}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;}remove方法
public V remove(Object key) { // 获取到该key对应的节点 和get相同 Entry<K,V> p = getEntry(key); if (p == null) return null; V oldValue = p.value; deleteEntry(p); return oldValue;}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. // 存在两个子树(左子树和右子树) if (p.left != null && p.right != null) { // 找到与p数值最接近的节点(即右子树的最左叶子节点) 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. // 找到所要替代的节点 Entry<K,V> replacement = (p.left != null ? p.left : p.right); if (replacement != null) { // Link replacement to parent // 替换节点 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 // 删除的节点为黑色节点，需要进行平衡 if (p.color == BLACK) fixAfterDeletion(replacement); } // 此时replacement为null(表明 p没有左子树也没有右子树)，如果p没有父节点，表明该树只有一个根节点 else if (p.parent == null) { // return if we are the only node. root = null; } // 此时replacement为null(表明 p没有左子树也没有右子树)，表明该节点为叶子节点 else { // No children. Use self as phantom replacement and unlink. // 删除的节点为黑色节点，需要进行平衡 if (p.color == BLACK) fixAfterDeletion(p); // 将p从树中移除 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; } }}static <K,V> TreeMap.Entry<K,V> successor(Entry<K,V> t) { if (t == null) return null; else if (t.right != null) { // 右节点不为null，找到后继节点(即右子树的左叶子节点) Entry<K,V> p = t.right; while (p.left != null) p = p.left; return p; } else { Entry<K,V> p = t.parent; Entry<K,V> ch = t; while (p != null && ch == p.right) { ch = p; p = p.parent; } return p; }}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);}由于本身的博客百度没有收录，博客地 />
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原文链id="treemap详解">TreeMap详解TreeMap是Map接口的一个实现类，底层基于红黑树的实现从继承机构可以看到TreeMap除了继承了AbstractMap类，还实现了NavigableMap接口，而NavigableMap接口是继承自SortedMap接口的，所以TreeMap是可以进行排序的关键变量//比较器，根据比较器来决定TreeMap的排序
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