TreeMap1.8源码

曾经终败给现在 2022-02-24 10:30 229阅读 0赞

## 使用 ##

TreeMap使用比较器排序，按照key的排序遍历，  
如果没有比较器，用默认比较器，key的类默认实现了Comparable接口的compareTo方法，比如Integer，String

key不能为null，value可以为null

Map<String, String> treeMap = new TreeMap<String, String>();
            treeMap.put("a", "1");
            treeMap.put("d", "4");
            treeMap.put("b", "2");
            treeMap.put("c", "3");
            treeMap.put("e", null);
            //treeMap.put(null, "f");//key不能为null
            System.out.println("TreeMap:" + treeMap);//TreeMap:{a=1, b=2, c=3, d=4, e=null}

TreeMap是非同步的（not synchronized），线程不安全的。如果需要在多线程环境使用，需要程序员手动同步；或者通过如下方式将TreeMap包装成（wrapped）同步的：

SortedMap m = Collections.synchronizedSortedMap(new TreeMap(...));

类

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

构造

//使用默认比较器
        public TreeMap() {
            comparator = null;
        }

用红黑树实现，Entry表示红黑树节点

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;
            }

## 查询 ##

从根节点向子节点遍历，逐个用比较器比较。如果比根节点大，就用右孩子继续比较，如果比根节点小，就用左孩子继续比较，否则是相等，就找到了。有点像后序遍历。

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);
            if (key == null)
                throw new NullPointerException();
            @SuppressWarnings("unchecked")
                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;
        }
        
         final Entry<K,V> getEntryUsingComparator(Object key) {
            @SuppressWarnings("unchecked")
                K k = (K) key;
            Comparator<? super K> cpr = comparator;
            if (cpr != null) {
                Entry<K,V> p = root;
                while (p != null) {
                    int cmp = cpr.compare(k, p.key);
                    if (cmp < 0)
                        p = p.left;
                    else if (cmp > 0)
                        p = p.right;
                    else
                        return p;
                }
            }
            return null;
        }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L21pbmd3dWxpcG8_size_16_color_FFFFFF_t_70]

## 添加 ##

public V put(K key, V value) {
            Entry<K,V> t = root;
            //添加第一个元素
            if (t == null) {
                compare(key, key); // type (and possibly null) check
    
                root = new Entry<>(key, value, null);
                size = 1;
                modCount++;
                return null;
            }
            //添加第二个元素
            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();
                @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);
            }
            Entry<K,V> e = new Entry<>(key, value, parent);
            if (cmp < 0)
                parent.left = e;
            else
                parent.right = e;
            fixAfterInsertion(e);
            size++;
            modCount++;
            return null;
        }

//红黑树调整函数fixAfterInsertion()
    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) {//如果y为null，则视为BLACK
                    setColor(parentOf(x), BLACK);              // 情况1
                    setColor(y, BLACK);                        // 情况1
                    setColor(parentOf(parentOf(x)), RED);      // 情况1
                    x = parentOf(parentOf(x));                 // 情况1
                } else {//没有叔叔
                    if (x == rightOf(parentOf(x))) {
                        x = parentOf(x);                       // 情况2
                        rotateLeft(x);                         // 情况2
                    }
                    setColor(parentOf(x), BLACK);              // 情况3
                    setColor(parentOf(parentOf(x)), RED);      // 情况3
                    rotateRight(parentOf(parentOf(x)));        // 情况3
                }
            } else {
                Entry<K,V> y = leftOf(parentOf(parentOf(x)));
                if (colorOf(y) == RED) {
                    setColor(parentOf(x), BLACK);              // 情况4
                    setColor(y, BLACK);                        // 情况4
                    setColor(parentOf(parentOf(x)), RED);      // 情况4
                    x = parentOf(parentOf(x));                 // 情况4
                } else {
                    if (x == leftOf(parentOf(x))) {
                        x = parentOf(x);                       // 情况5
                        rotateRight(x);                        // 情况5
                    }
                    setColor(parentOf(x), BLACK);              // 情况6
                    setColor(parentOf(parentOf(x)), RED);      // 情况6
                    rotateLeft(parentOf(parentOf(x)));         // 情况6
                }
            }
        }
        root.color = BLACK;
    }

举例  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L21pbmd3dWxpcG8_size_16_color_FFFFFF_t_70 1]  
添加5个元素示意图  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L21pbmd3dWxpcG8_size_16_color_FFFFFF_t_70 2]

## 删除 ##

public V remove(Object key) {
            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.
            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;//只有一个根节点，置为null就是删除
            } 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;//删除父子节点间的连接，就是删除节点
                    else if (p == p.parent.right)
                        p.parent.right = null;
                    p.parent = null;//删除父子节点间的连接，就是删除节点
                }
            }
        }

寻找后继节点，就是比较器排序，比当前节点大的后一个节点

static <K,V> TreeMap.Entry<K,V> successor(Entry<K,V> t) {
            if (t == null)
                return null;
            else if (t.right != null) {
                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;
            }
        }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L21pbmd3dWxpcG8_size_16_color_FFFFFF_t_70 3]  
删除举例  
删除c，直接删除

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