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手撕 HashMap 源码
发布于: 2 小时前
文章已同步至 GitHub 开源项目: Java超神之路
HashMap 一直是面试的重点。今天我们来了解了解它的源码吧！
首先看一下 Map 的继承结构图
源码分析
/* * HashMap结构：哈希数组+链表/红黑树，key和value均可以为null * * 存储元素时，需要调用key的hashCode()方法，计算出一个哈希值 * 1.哈希值相同的元素，必定位于同一个哈希槽（链）上，但不能确定这两个元素是不是同位元素 * 在进一步判断key如果相等（必要时需要调用equals()方法）时，才能确定这两个元素属于同位元素 * 如果是存储同位元素，需要考虑是否允许覆盖旧值的问题 * 2.哈希值不同的元素，它们也可能位于同一个哈希槽（链）上，但它们肯定不是同位元素 * * 注：HashMap非线程安全。如果需要考虑并发，则需要使用ConcurrentHashMap */public class HashMap<K,V> extends AbstractMap<K,V> implements Map<K,V>, Cloneable, Serializable { /** * The maximum capacity, used if a higher value is implicitly specified * by either of the constructors with arguments. * MUST be a power of two <= 1<<30. */ static final int MAXIMUM_CAPACITY = 1 << 30; // 哈希数组最大容量 /** * The default initial capacity - MUST be a power of two. */ static final int DEFAULT_INITIAL_CAPACITY = 16; // 哈希数组默认容量 /** * The load factor used when none specified in constructor. */ static final float DEFAULT_LOAD_FACTOR = 0.75f; // HashMap默认装载因子（负荷系数） /** * The bin count threshold for using a tree rather than list for a * bin. Bins are converted to trees when adding an element to a * bin with at least this many nodes. The value must be greater * than 2 and should be at least 8 to mesh with assumptions in * tree removal about conversion back to plain bins upon * shrinkage. */ static final int TREEIFY_THRESHOLD = 8; // 某个哈希槽（链）上的元素数量增加到此值后，这些元素进入波动期，即将从链表转换为红黑树 /** * The smallest table capacity for which bins may be treeified. * (Otherwise the table is resized if too many nodes in a bin.) * Should be at least 4 * TREEIFY_THRESHOLD to avoid conflicts * between resizing and treeification thresholds. */ static final int MIN_TREEIFY_CAPACITY = 64; // 哈希数组的容量至少增加到此值，且满足TREEIFY_THRESHOLD的要求时，将链表转换为红黑树 /** * The bin count threshold for untreeifying a (split) bin during a * resize operation. Should be less than TREEIFY_THRESHOLD, and at * most 6 to mesh with shrinkage detection under removal. */ static final int UNTREEIFY_THRESHOLD = 6; // 哈希槽（链）上的红黑树上的元素数量减少到此值时，将红黑树转换为链表 /** * The table, initialized on first use, and resized as * necessary. When allocated, length is always a power of two. * (We also tolerate length zero in some operations to allow * bootstrapping mechanics that are currently not needed.) */ transient Node<K,V>[] table; // 哈希数组（注：哈希数组的容量跟HashMap可以存储的元素数量不是一回事） /** * The number of key-value mappings contained in this map. */ transient int size; // HashMap中的元素数量 /** * The load factor for the hash table. * * @serial */ final float loadFactor; // HashMap当前使用的装载因子 /** * The next size value at which to resize (capacity * load factor). * * @serial * * The javadoc description is true upon serialization. * Additionally, if the table array has not been allocated, this field holds the initial array capacity, * or zero signifying DEFAULT_INITIAL_CAPACITY. */ int threshold; // HashMap扩容阈值，【一般】由（哈希数组容量*HashMap装载因子）计算而来，HashMap中元素数量超过该阈值时，哈希数组需要扩容 /** * Holds cached entrySet(). Note that AbstractMap fields are used * for keySet() and values(). */ transient Set<Map.Entry<K,V>> entrySet; // entry集合 /** * The number of times this HashMap has been structurally modified * Structural modifications are those that change the number of mappings in * the HashMap or otherwise modify its internal structure (e.g., * rehash). This field is used to make iterators on Collection-views of * the HashMap fail-fast. (See ConcurrentModificationException). */ transient int modCount; // 记录HashMap结构的修改次数 /*▼ 构造器 ████████████████████████████████████████████████████████████████████████████████┓ */ /** * Constructs an empty {@code HashMap} with the default initial capacity (16) and the default load factor (0.75). */ // 初始化一个哈希数组容量为16，装载因子为0.75的HashMap public HashMap() { this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted } /** * Constructs an empty {@code HashMap} with the specified initial * capacity and the default load factor (0.75). * * @param initialCapacity the initial capacity. * @throws IllegalArgumentException if the initial capacity is negative. */ // 初始化一个哈希数组容量为initialCapacity，装载因子为0.75的HashMap public HashMap(int initialCapacity) { this(initialCapacity, DEFAULT_LOAD_FACTOR); } /** * Constructs an empty {@code HashMap} with the specified initial * capacity and load factor. * * @param initialCapacity the initial capacity * @param loadFactor the load factor * @throws IllegalArgumentException if the initial capacity is negative * or the load factor is nonpositive */ // 初始化一个哈希数组容量为initialCapacity，装载因子为loadFactor的HashMap public HashMap(int initialCapacity, float loadFactor) { if (initialCapacity < 0) { throw new IllegalArgumentException("Illegal initial capacity: " + initialCapacity); } if (initialCapacity > MAXIMUM_CAPACITY) { initialCapacity = MAXIMUM_CAPACITY; } if (loadFactor <= 0 || Float.isNaN(loadFactor)) { throw new IllegalArgumentException("Illegal load factor: " + loadFactor); } // 初始化装载因子 this.loadFactor = loadFactor; // 用初始容量信息来初始化HashMap扩容阈值，该阈值后续将作为初始化哈希数组的容量依据 this.threshold = tableSizeFor(initialCapacity); } /** * Constructs a new {@code HashMap} with the same mappings as the * specified {@code Map}. The {@code HashMap} is created with * default load factor (0.75) and an initial capacity sufficient to * hold the mappings in the specified {@code Map}. * * @param m the map whose mappings are to be placed in this map * @throws NullPointerException if the specified map is null */ // 使用指定的HashMap中的元素来初始化一个新的HashMap public HashMap(Map<? extends K, ? extends V> m) { this.loadFactor = DEFAULT_LOAD_FACTOR; // 将指定HashMap中的元素存入到当前HashMap（允许覆盖） putMapEntries(m, false); } /*▲ 构造器 ████████████████████████████████████████████████████████████████████████████████┛ */ /*▼ 存值 ████████████████████████████████████████████████████████████████████████████████┓ */ /** * Associates the specified value with the specified key in this map. * If the map previously contained a mapping for the key, the old * value is replaced. * * @param key key with which the specified value is to be associated * @param value value to be associated with the specified key * @return the previous value associated with {@code key}, or * {@code null} if there was no mapping for {@code key}. * (A {@code null} return can also indicate that the map * previously associated {@code null} with {@code key}.) */ // 将指定的元素（key-value）存入HashMap，并返回旧值，允许覆盖 public V put(K key, V value) { return putVal(hash(key), key, value, false, true); } // 将指定的元素（key-value）存入HashMap，并返回旧值，不允许覆盖 @Override public V putIfAbsent(K key, V value) { return putVal(hash(key), key, value, true, true); } /** * Copies all of the mappings from the specified map to this map. * These mappings will replace any mappings that this map had for * any of the keys currently in the specified map. * * @param m mappings to be stored in this map * * @throws NullPointerException if the specified map is null */ // 将指定Map中的元素存入到当前Map（允许覆盖） public void putAll(Map<? extends K, ? extends V> map) { putMapEntries(map, true); } /*▲ 存值 ████████████████████████████████████████████████████████████████████████████████┛ */ /*▼ 取值 ████████████████████████████████████████████████████████████████████████████████┓ */ /** * Returns the value to which the specified key is mapped, * or {@code null} if this map contains no mapping for the key. * * <p>More formally, if this map contains a mapping from a key * {@code k} to a value {@code v} such that {@code (key==null ? k==null : * key.equals(k))}, then this method returns {@code v}; otherwise * it returns {@code null}. (There can be at most one such mapping.) * * <p>A return value of {@code null} does not <i>necessarily</i> * indicate that the map contains no mapping for the key; it's also * possible that the map explicitly maps the key to {@code null}. * The {@link #containsKey containsKey} operation may be used to * distinguish these two cases. * * @see #put(Object, Object) */ // 根据指定的key获取对应的value，如果不存在，则返回null public V get(Object key) { // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null Node<K,V> e = getNode(hash(key), key); return e == null ? null : e.value; } // 根据指定的key获取对应的value，如果不存在，则返回指定的默认值defaultValue @Override public V getOrDefault(Object key, V defaultValue) { // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null Node<K,V> e = getNode(hash(key), key); return e == null ? defaultValue : e.value; } /*▲ 取值 ████████████████████████████████████████████████████████████████████████████████┛ */ /*▼ 移除 ████████████████████████████████████████████████████████████████████████████████┓ */ /** * Removes the mapping for the specified key from this map if present. * * @param key key whose mapping is to be removed from the map * * @return the previous value associated with {@code key}, or * {@code null} if there was no mapping for {@code key}. * (A {@code null} return can also indicate that the map * previously associated {@code null} with {@code key}.) */ // 移除拥有指定key的元素，并返回刚刚移除的元素的值 public V remove(Object key) { Node<K, V> e; return (e = removeNode(hash(key), key, null, false, true)) == null ? null : e.value; } // 移除拥有指定key和value的元素，返回值表示是否移除成功 @Override public boolean remove(Object key, Object value) { return removeNode(hash(key), key, value, true, true) != null; } /** * Removes all of the mappings from this map. * The map will be empty after this call returns. */ // 清空HashMap中所有元素 public void clear() { Node<K, V>[] tab; modCount++; if((tab = table) != null && size>0) { size = 0; Arrays.fill(tab, null); } } /*▲ 移除 ████████████████████████████████████████████████████████████████████████████████┛ */ /*▼ 替换 ████████████████████████████████████████████████████████████████████████████████┓ */ // 将拥有指定key的元素的值替换为newValue，并返回刚刚替换的元素的值（替换失败返回null） @Override public V replace(K key, V newValue) { // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null Node<K,V> e = getNode(hash(key), key); if (e != null) { V oldValue = e.value; e.value = newValue; afterNodeAccess(e); return oldValue; } return null; } // 将拥有指定key和oldValue的元素的值替换为newValue，返回值表示是否成功替换 @Override public boolean replace(K key, V oldValue, V newValue) { // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null Node<K,V> e = getNode(hash(key), key); V v; if (e != null && ((v = e.value) == oldValue || (v != null && v.equals(oldValue)))) { e.value = newValue; afterNodeAccess(e); return true; } return false; } // 替换当前HashMap中的所有元素，替换策略由function决定，function的入参是元素的key和value，出参作为新值 @Override public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) { Node<K,V>[] tab; if (function == null) { throw new NullPointerException(); } if (size > 0 && (tab = table) != null) { int mc = modCount; for (Node<K,V> e : tab) { for (; e != null; e = e.next) { e.value = function.apply(e.key, e.value); } } if (modCount != mc) { throw new ConcurrentModificationException(); } } } /*▲ 替换 ████████████████████████████████████████████████████████████████████████████████┛ */ /*▼ 包含查询 ████████████████████████████████████████████████████████████████████████████████┓ */ /** * Returns {@code true} if this map contains a mapping for the * specified key. * * @param key The key whose presence in this map is to be tested * * @return {@code true} if this map contains a mapping for the specified * key. */ // 判断HashMap中是否存在指定key的元素 public boolean containsKey(Object key) { // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null Node<K,V> e = getNode(hash(key), key); return e != null; } /** * Returns {@code true} if this map maps one or more keys to the * specified value. * * @param value value whose presence in this map is to be tested * * @return {@code true} if this map maps one or more keys to the * specified value */ // 判断HashMap中是否存在指定value的元素 public boolean containsValue(Object value) { Node<K, V>[] tab; V v; if((tab = table) != null && size>0) { for(Node<K, V> e : tab) { for(; e != null; e = e.next) { if((v = e.value) == value || (value != null && value.equals(v))) { return true; } } } } return false; } /*▲ 包含查询 ████████████████████████████████████████████████████████████████████████████████┛ */ /*▼ 视图 ████████████████████████████████████████████████████████████████████████████████┓ */ /** * Returns a {@link Set} view of the keys contained in this map. * The set is backed by the map, so changes to the map are * reflected in the set, and vice-versa. If the map is modified * while an iteration over the set is in progress (except through * the iterator's own {@code remove} operation), the results of * the iteration are undefined. The set supports element removal, * which removes the corresponding mapping from the map, via the * {@code Iterator.remove}, {@code Set.remove}, * {@code removeAll}, {@code retainAll}, and {@code clear} * operations. It does not support the {@code add} or {@code addAll} * operations. * * @return a set view of the keys contained in this map */ // 获取HashMap中key的集合 public Set<K> keySet() { Set<K> ks = keySet; if(ks == null) { ks = new KeySet(); keySet = ks; } return ks; } /** * Returns a {@link Collection} view of the values contained in this map. * The collection is backed by the map, so changes to the map are * reflected in the collection, and vice-versa. If the map is * modified while an iteration over the collection is in progress * (except through the iterator's own {@code remove} operation), * the results of the iteration are undefined. The collection * supports element removal, which removes the corresponding * mapping from the map, via the {@code Iterator.remove}, * {@code Collection.remove}, {@code removeAll}, * {@code retainAll} and {@code clear} operations. It does not * support the {@code add} or {@code addAll} operations. * * @return a view of the values contained in this map */ // 获取HashMap中value的集合 public Collection<V> values() { Collection<V> vs = values; if(vs == null) { vs = new Values(); values = vs; } return vs; } /** * Returns a {@link Set} view of the mappings contained in this map. * The set is backed by the map, so changes to the map are * reflected in the set, and vice-versa. If the map is modified * while an iteration over the set is in progress (except through * the iterator's own {@code remove} operation, or through the * {@code setValue} operation on a map entry returned by the * iterator) the results of the iteration are undefined. The set * supports element removal, which removes the corresponding * mapping from the map, via the {@code Iterator.remove}, * {@code Set.remove}, {@code removeAll}, {@code retainAll} and * {@code clear} operations. It does not support the * {@code add} or {@code addAll} operations. * * @return a set view of the mappings contained in this map */ // 获取HashMap中key-value对的集合 public Set<Map.Entry<K, V>> entrySet() { Set<Map.Entry<K, V>> es; return (es = entrySet) == null ? (entrySet = new EntrySet()) : es; } /*▲ 视图 ████████████████████████████████████████████████████████████████████████████████┛ */ /*▼ 遍历 ████████████████████████████████████████████████████████████████████████████████┓ */ // 遍历HashMap中的元素，并对其应用action操作，action的入参是元素的key和value @Override public void forEach(BiConsumer<? super K, ? super V> action) { Node<K, V>[] tab; if(action == null) { throw new NullPointerException(); } if(size>0 && (tab = table) != null) { int mc = modCount; for(Node<K, V> e : tab) { for(; e != null; e = e.next) { action.accept(e.key, e.value); } } if(modCount != mc) { throw new ConcurrentModificationException(); } } } /*▲ 遍历 ████████████████████████████████████████████████████████████████████████████████┛ */ /*▼ 重新映射 ████████████████████████████████████████████████████████████████████████████████┓ */ /** * {@inheritDoc} * * <p>This method will, on a best-effort basis, throw a * {@link ConcurrentModificationException} if it is detected that the * remapping function modifies this map during computation. * * @throws ConcurrentModificationException if it is detected that the * remapping function modified this map */ /* * 插入/删除/替换操作，返回新值（可能为null） * 此方法的主要意图：使用备用value和旧value创造的新value来更新旧value * * 注：以下流程图中，涉及到判断(◇)时，纵向代表【是】，横向代表【否】。此外，使用★代表计算。 * * ●查找同位元素● * | * ↓ * ◇存在同位元素◇ --→ ★新value=备用value★ --→ ■【插入】新value■ * | 是 否 * ↓ * ◇旧value不为null --→ ★新value=备用value★ --→ ■新value【替换】旧value■ * | 是 否 * ↓ * ★新value=(旧value, 备用value)★ * | * ↓ * ◇新value不为null◇ --→ ■【删除】同位元素■ * | 是 否 * ↓ * ■新value【替换】旧value■ */ @Override public V merge(K key, V bakValue, BiFunction<? super V, ? super V, ? extends V> remappingFunction) { if(bakValue == null) { throw new NullPointerException(); } if(remappingFunction == null) { throw new NullPointerException(); } int hash = hash(key); Node<K, V>[] tab; Node<K, V> first; int n, i; int binCount = 0; TreeNode<K, V> t = null; Node<K, V> old = null; if(size>threshold || (tab = table) == null || (n = tab.length) == 0) { // 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组 tab = resize(); n = tab.length; } // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null if((first = tab[i = (n - 1) & hash]) != null) { if(first instanceof TreeNode) { old = (t = (TreeNode<K, V>) first).getTreeNode(hash, key); } else { Node<K, V> e = first; K k; do { if(e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) { old = e; break; } ++binCount; } while((e = e.next) != null); } } // 如果找到了同位元素 if(old != null) { V newValue; // 确定应用到目标元素上的新值 if(old.value != null) { int mc = modCount; newValue = remappingFunction.apply(old.value, bakValue); if(mc != modCount) { throw new ConcurrentModificationException(); } } else { newValue = bakValue; } // 如果新值不为null，直接替换旧值 if(newValue != null) { old.value = newValue; afterNodeAccess(old); } else { // 如果新值为null，则会移除该元素 removeNode(hash, key, null, false, true); } return newValue; } // 如果没找到目标元素，但是传入的value不为null，则向HashMap中插入新元素 if(bakValue != null) { if(t != null) { t.putTreeVal(this, tab, hash, key, bakValue); } else { tab[i] = newNode(hash, key, bakValue, first); if(binCount >= TREEIFY_THRESHOLD - 1) { treeifyBin(tab, hash); } } ++modCount; ++size; afterNodeInsertion(true); } return bakValue; } /** * {@inheritDoc} * * <p>This method will, on a best-effort basis, throw a * {@link ConcurrentModificationException} if it is detected that the * remapping function modifies this map during computation. * * @throws ConcurrentModificationException if it is detected that the * remapping function modified this map */ /* * 插入/删除/替换操作，返回新值（可能为null） * 此方法的主要意图：使用key和旧value创造的新value来更新旧value * * 注：以下流程图中，涉及到判断(◇)时，纵向代表【是】，横向代表【否】。此外，使用★代表计算。 * * ●查找同位元素● * | * ↓ * ◇存在同位元素◇ --→ ★新value=(key, null)★ * | 是 否 | * ↓ | * ★新value=(key, 旧value)★ | * ├---------------------------┘ * ↓ * ◇新value不为null◇ --→ ■如果存在同位元素，则【删除】同位元素■ * | 是 否 * ↓ * ■ 存在同位元素，则新value【替换】旧value■ * ■不存在同位元素，则【插入】新value ■ */ @Override public V compute(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { if(remappingFunction == null) { throw new NullPointerException(); } int hash = hash(key); Node<K, V>[] tab; Node<K, V> first; int n, i; int binCount = 0; TreeNode<K, V> t = null; Node<K, V> old = null; if(size>threshold || (tab = table) == null || (n = tab.length) == 0) { // 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组 tab = resize(); n = tab.length; } // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null if((first = tab[i = (n - 1) & hash]) != null) { if(first instanceof TreeNode) { old = (t = (TreeNode<K, V>) first).getTreeNode(hash, key); } else { Node<K, V> e = first; K k; do { if(e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) { old = e; break; } ++binCount; } while((e = e.next) != null); } } V oldValue = (old == null) ? null : old.value; int mc = modCount; // 利用key和旧的value计算一个新的value V newValue = remappingFunction.apply(key, oldValue); if(mc != modCount) { throw new ConcurrentModificationException(); } // 如果存在同位元素 if(old != null) { if(newValue != null) { old.value = newValue; afterNodeAccess(old); } else { removeNode(hash, key, null, false, true); } } else if(newValue != null) { if(t != null) { t.putTreeVal(this, tab, hash, key, newValue); } else { tab[i] = newNode(hash, key, newValue, first); if(binCount >= TREEIFY_THRESHOLD - 1) { treeifyBin(tab, hash); } } modCount = mc + 1; ++size; afterNodeInsertion(true); } return newValue; } /** * {@inheritDoc} * * <p>This method will, on a best-effort basis, throw a * {@link ConcurrentModificationException} if it is detected that the * remapping function modifies this map during computation. * * @throws ConcurrentModificationException if it is detected that the * remapping function modified this map */ /* * 删除/替换操作，返回新值（可能为null） * 此方法的主要意图：存在同位元素，且旧value不为null时，使用key和旧value创造的新value来更新旧value * * 注：以下流程图中，涉及到判断(◇)时，纵向代表【是】，横向代表【否】。此外，使用★代表计算。 * * ●查找同位元素● * | * ↓ * ◇存在同位元素 && 旧value不为null◇ * | * ↓ * ★新value=(key, 旧value)★ * | * ↓ * ◇新value不为null◇ --→ ■【删除】同位元素■ * | * ↓ * ■新value【替换】旧value■ */ @Override public V computeIfPresent(K key, BiFunction<? super K, ? super V, ? extends V> remappingFunction) { if(remappingFunction == null) { throw new NullPointerException(); } // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null Node<K, V> e = getNode(hash(key), key); V oldValue; // 如果同位元素存在，且旧的值不为null if(e != null && (oldValue = e.value) != null) { int mc = modCount; // 利用key和旧的value计算一个新的value V newValue = remappingFunction.apply(key, oldValue); if(mc != modCount) { throw new ConcurrentModificationException(); } // 如果新的value不为null，则【替换】 if(newValue != null) { e.value = newValue; afterNodeAccess(e); return newValue; } // 如果新的value为null，则【删除】 removeNode(hash(key), key, null, false, true); } return null; } /** * {@inheritDoc} * * <p>This method will, on a best-effort basis, throw a * {@link ConcurrentModificationException} if it is detected that the * mapping function modifies this map during computation. * * @throws ConcurrentModificationException if it is detected that the * mapping function modified this map */ /* * 插入/替换操作，返回新值（可能为null） * 此方法的主要意图：不存在同位元素，或旧value为null时，使用key创造的新value来更新旧value。如果同位元素旧值不为空，则直接返回旧值。 * * 注：以下流程图中，涉及到判断(◇)时，纵向代表【是】，横向代表【否】。此外，使用★代表计算。 * * ●查找同位元素● * | * ↓ * ◇存在同位元素 && 旧value不为null◇ --→ ★新value=(key)★ * 否 | * ↓ * ◇新value不为null◇ * | * ↓ * ■ 存在同位元素，则新value【替换】旧value■ * ■不存在同位元素，则【插入】新value ■ */ @Override public V computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction) { if(mappingFunction == null) { throw new NullPointerException(); } int hash = hash(key); Node<K, V>[] tab; Node<K, V> first; int n, i; int binCount = 0; TreeNode<K, V> t = null; Node<K, V> old = null; if(size>threshold || (tab = table) == null || (n = tab.length) == 0) { // 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组 tab = resize(); n = tab.length; } // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null if((first = tab[i = (n - 1) & hash]) != null) { if(first instanceof TreeNode) { old = (t = (TreeNode<K, V>) first).getTreeNode(hash, key); } else { Node<K, V> e = first; K k; do { if(e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) { old = e; break; } ++binCount; } while((e = e.next) != null); } V oldValue; // 如果同位元素存在，且旧的value不是null，直接返回 if(old != null && (oldValue = old.value) != null) { afterNodeAccess(old); return oldValue; } } int mc = modCount; // 对key应用mappingFunction函数，计算出一个新的value V newValue = mappingFunction.apply(key); if(mc != modCount) { throw new ConcurrentModificationException(); } // 新的value为null if(newValue == null) { return null; } // 同位元素存在，且旧的value为null，新的value不为null，则用新的value【替换】旧的value if(old != null) { old.value = newValue; afterNodeAccess(old); return newValue; } // 如果不存在同位元素，则【插入】key和新的value为一个新元素 if(t != null) { t.putTreeVal(this, tab, hash, key, newValue); } else { tab[i] = newNode(hash, key, newValue, first); if(binCount >= TREEIFY_THRESHOLD - 1) { treeifyBin(tab, hash); } } modCount = mc + 1; ++size; afterNodeInsertion(true); return newValue; } /*▲ 重新映射 ████████████████████████████████████████████████████████████████████████████████┛ */ /*▼ LinkedHashMap ████████████████████████████████████████████████████████████████████████████████┓ */ /* * The following package-protected methods are designed to be overridden by LinkedHashMap, but not by any other subclass. * Nearly all other internal methods are also package-protected but are declared final, so can be used by LinkedHashMap, view classes, and HashSet. */ // 创建一个普通Node Node<K, V> newNode(int hash, K key, V value, Node<K, V> next) { return new Node<>(hash, key, value, next); } // 创建一个红黑树的TreeNode TreeNode<K, V> newTreeNode(int hash, K key, V value, Node<K, V> next) { return new TreeNode<>(hash, key, value, next); } // 从红黑树的TreeNode转换为一个普通Node Node<K, V> replacementNode(Node<K, V> p, Node<K, V> next) { return new Node<>(p.hash, p.key, p.value, next); } // 从普通Node转换为一个红黑树的TreeNode TreeNode<K, V> replacementTreeNode(Node<K, V> p, Node<K, V> next) { return new TreeNode<>(p.hash, p.key, p.value, next); } /** * Reset to initial default state. Called by clone and readObject. */ // 重置当前HashMap，清空一切参数 void reinitialize() { table = null; entrySet = null; keySet = null; values = null; modCount = 0; threshold = 0; size = 0; } // 插入一个新元素时的回调 void afterNodeInsertion(boolean evict) { } // 移除一个新元素时的回调 void afterNodeRemoval(Node<K, V> p) { } // 访问一个新元素时的回调 void afterNodeAccess(Node<K, V> p) { } /* Called only from writeObject, to ensure compatible ordering */ // 用于序列化过程 void internalWriteEntries(ObjectOutputStream s) throws IOException { Node<K,V>[] tab; if (size > 0 && (tab = table) != null) { for (Node<K,V> e : tab) { for (; e != null; e = e.next) { s.writeObject(e.key); s.writeObject(e.value); } } } } /*▲ LinkedHashMap ████████████████████████████████████████████████████████████████████████████████┛ */ /*▼ 杂项 ████████████████████████████████████████████████████████████████████████████████┓ */ /** * Returns the number of key-value mappings in this map. * * @return the number of key-value mappings in this map */ // 获取HashMap中的元素数量 public int size() { return size; } /** * Returns {@code true} if this map contains no key-value mappings. * * @return {@code true} if this map contains no key-value mappings */ // 判断HashMap是否为空集 public boolean isEmpty() { return size == 0; } /*▲ 杂项 ████████████████████████████████████████████████████████████████████████████████┛ */ /*▼ 序列化 ████████████████████████████████████████████████████████████████████████████████┓ */ private static final long serialVersionUID = 362498820763181265L; /** * Saves this map to a stream (that is, serializes it). * * @param s the stream * * @throws IOException if an I/O error occurs * @serialData The <i>capacity</i> of the HashMap (the length of the * bucket array) is emitted (int), followed by the * <i>size</i> (an int, the number of key-value * mappings), followed by the key (Object) and value (Object) * for each key-value mapping. The key-value mappings are * emitted in no particular order. */ private void writeObject(java.io.ObjectOutputStream s) throws IOException { int buckets = capacity(); // Write out the threshold, loadfactor, and any hidden stuff s.defaultWriteObject(); s.writeInt(buckets); s.writeInt(size); internalWriteEntries(s); } /** * Reconstitutes this map from a stream (that is, deserializes it). * * @param s the stream * * @throws ClassNotFoundException if the class of a serialized object * could not be found * @throws IOException if an I/O error occurs */ private void readObject(java.io.ObjectInputStream s) throws IOException, ClassNotFoundException { // Read in the threshold (ignored), loadfactor, and any hidden stuff s.defaultReadObject(); reinitialize(); if(loadFactor<=0 || Float.isNaN(loadFactor)) { throw new InvalidObjectException("Illegal load factor: " + loadFactor); } s.readInt(); // Read and ignore number of buckets int mappings = s.readInt(); // Read number of mappings (size) if(mappings<0) { throw new InvalidObjectException("Illegal mappings count: " + mappings); } else if(mappings>0) { // (if zero, use defaults) // Size the table using given load factor only if within // range of 0.25...4.0 float lf = Math.min(Math.max(0.25f, loadFactor), 4.0f); float fc = (float) mappings / lf + 1.0f; int cap = ((fc<DEFAULT_INITIAL_CAPACITY) ? DEFAULT_INITIAL_CAPACITY : (fc >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : tableSizeFor((int) fc)); float ft = (float) cap * lf; threshold = ((cap<MAXIMUM_CAPACITY && ft<MAXIMUM_CAPACITY) ? (int) ft : Integer.MAX_VALUE); // Check Map.Entry[].class since it's the nearest public type to // what we're actually creating. SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Map.Entry[].class, cap); @SuppressWarnings({"rawtypes", "unchecked"}) Node<K, V>[] tab = (Node<K, V>[]) new Node[cap]; table = tab; // Read the keys and values, and put the mappings in the HashMap for(int i = 0; i<mappings; i++) { @SuppressWarnings("unchecked") K key = (K) s.readObject(); @SuppressWarnings("unchecked") V value = (V) s.readObject(); putVal(hash(key), key, value, false, false); } } } /*▲ 序列化 ████████████████████████████████████████████████████████████████████████████████┛ */ /** * Returns a shallow copy of this {@code HashMap} instance: the keys and * values themselves are not cloned. * * @return a shallow copy of this map */ @SuppressWarnings("unchecked") @Override public Object clone() { HashMap<K, V> result; try { result = (HashMap<K, V>) super.clone(); } catch(CloneNotSupportedException e) { // this shouldn't happen, since we are Cloneable throw new InternalError(e); } result.reinitialize(); // 将当前HashMap中的元素存入到result（允许覆盖） result.putMapEntries(this, false); return result; } /** * Computes key.hashCode() and spreads (XORs) higher bits of hash to lower. * Because the table uses power-of-two masking, sets of hashes that vary only in bits above the current mask will always collide. * (Among known examples are sets of Float keys holding consecutive whole numbers in small tables.) * So we apply a transform that spreads the impact of higher bits downward. * There is a tradeoff between speed, utility, and quality of bit-spreading. * Because many common sets of hashes are already reasonably distributed (so don't benefit from spreading), * and because we use trees to handle large sets of collisions in bins, * we just XOR some shifted bits in the cheapest possible way to reduce systematic lossage, * as well as to incorporate impact of the highest bits that would otherwise never be used in index calculations because of table bounds. */ /* * 计算key的哈希值，在这个过程中会调用key的hashCode()方法 * * key是一个对象的引用（可以看成地址） * 理论上讲，key的值是否相等，跟计算出的哈希值是否相等，没有必然联系，一切都取决于hashCode()这个方法 */ static final int hash(Object key) { int h; return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16); } /** * Returns x's Class if it is of the form "class C implements * Comparable<C>", else null. */ /* * 检查Comparable接口是否有效 * * 假设存在X类型的实例x， * 如果X类型实现了Comparable接口，且接口中的类型参数是X自身，则返回X.class， * 否则，将返回null，这代表X没有实现“有效”的Comparable接口 * * 例如： * class X implements Comparable<X> { * // 。。。 * } * * X x = new X(); * * 则：comparableClassFor(x)返回X.class */ static Class<?> comparableClassFor(Object x) { // 是否实现了Comparable接口 if(x instanceof Comparable) { Class<?> c = x.getClass(); // 快速判断。对于String类型的实例，则直接返回String.class if(c == String.class) { // bypass checks return c; } // 获取当前类的父接口（可识别泛型类型和非泛型类型） Type[] ts = c.getGenericInterfaces(); if(ts != null) { for(Type t : ts) { if(t instanceof ParameterizedType) { ParameterizedType p = (ParameterizedType) t; if(p.getRawType() == Comparable.class){ // 获取参数化类型中的实际参数（argument） Type[] as = p.getActualTypeArguments(); if(as != null) { if(as.length == 1){ /* * 进一步判断，是否实现了“有效”的Comparable接口， * “有效”的含义是，Comparable接口的参数为该类本身， * 因为只有这样，才能对该类进行有效的内部比较 */ if(as[0] == c){ // type arg is c return c; } } } } } } } } return null; } /** * Returns k.compareTo(x) if x matches kc (k's screened comparable class), else 0. */ // 返回k和x的比较结果 @SuppressWarnings({"rawtypes", "unchecked"}) // for cast to Comparable static int compareComparables(Class<?> kc, Object k, Object x) { return x == null || x.getClass() != kc ? 0 : ((Comparable) k).compareTo(x); } /** * Returns a power of two size for the given target capacity. */ /* * 根据预期的容量cap计算出HashMap中的哈希数组实际需要分配的容量 * 如果输入值是2的冪，则原样返回，如果不是2的冪，则向上取就近的冪 * 比如输入13，返回16，输入17，返回32 */ static final int tableSizeFor(int cap) { int n = -1 >>> Integer.numberOfLeadingZeros(cap - 1); return (n<0) ? 1 : (n >= MAXIMUM_CAPACITY) ? MAXIMUM_CAPACITY : n + 1; } /** * Implements Map.putAll and Map constructor. * * @param m the map * @param evict false when initially constructing this map, else true (relayed to method afterNodeInsertion). */ // 将指定HashMap中的元素存入到当前HashMap（允许覆盖） final void putMapEntries(Map<? extends K, ? extends V> map, boolean evict) { int s = map.size(); if(s>0) { // 如果当前HashMap的哈希数组还未初始化 if(table == null) { // pre-size // 由HashMap中的元素数量反推哈希数组的最低容量要求 float ft = ((float) s / loadFactor) + 1.0F; int t = ((ft<(float) MAXIMUM_CAPACITY) ? (int) ft : MAXIMUM_CAPACITY); // 计算HashMap扩容阈值 if(t>threshold) { threshold = tableSizeFor(t); } // 如果当前HashMap的哈希数组已存在，但是容量不足，则需要扩容 } else if(s>threshold) { // 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组 resize(); } for(Map.Entry<? extends K, ? extends V> e : map.entrySet()) { K key = e.getKey(); V value = e.getValue(); // 向HashMap中存入新的元素，允许覆盖 putVal(hash(key), key, value, false, evict); } } } /** * Implements Map.get and related methods. * * @param hash hash for key * @param key the key * * @return the node, or null if none */ // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null final Node<K, V> getNode(int hash, Object key) { Node<K, V>[] tab; Node<K, V> first, e; int n; K k; if((tab = table) != null && (n = tab.length)>0 && (first = tab[(n - 1) & hash]) != null) { /* * 对哈希槽（链）中的首个元素进行判断 * * 只有哈希值一致（还说明不了key是否一致），且key也相同（必要时需要用到equals()方法）时， * 这里才认定是存在同位元素（在HashMap中占据相同位置的元素） */ if(first.hash == hash && // always check first node ((k = first.key) == key || (key != null && key.equals(k)))) { return first; } if((e = first.next) != null) { // 如果是红黑树元素，则在红黑树中查找 if(first instanceof TreeNode) { return ((TreeNode<K, V>) first).getTreeNode(hash, key); } // 遍历哈希槽（链）上后续的元素 do { if(e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) { return e; } } while((e = e.next) != null); } } return null; } /** * Implements Map.put and related methods. * * @param hash hash for key * @param key the key * @param value the value to put * @param onlyIfAbsent if true, don't change existing value * @param evict if false, the table is in creation mode. * * @return previous value, or null if none */ /* * 向当前Map中存入新的元素，并返回旧元素 * * hash key的哈希值 * onlyIfAbsent 是否需要维持原状（不覆盖旧值） * evict if false, the table is in creation mode. * * 返回同位元素的旧值（在当前Map中占据相同位置的元素） * 如果不存在同位元素，即插入了新元素，则返回null * 如果存在同位元素，但同位元素的旧值为null，那么也返回null */ final V putVal(int hash, K key, V value, boolean onlyIfAbsent, boolean evict) { Node<K, V>[] tab; // 指向当前哈希数组 Node<K, V> p; // 指向待插入元素应当插入的位置 int n, i; // 如果哈希数组还未初始化，或者容量无效，则需要初始化一个哈希数组 if((tab = table) == null || (n = tab.length) == 0) { // 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组 tab = resize(); n = tab.length; } // p指向hash所在的哈希槽（链）上的首个元素 p = tab[i = (n - 1) & hash]; // 如果哈希槽为空，则在该槽上放置首个元素（普通Node） if(p == null) { tab[i] = newNode(hash, key, value, null); // 如果哈希槽不为空，则需要在哈希槽后面链接更多的元素 } else { Node<K, V> e; K k; /* * 对哈希槽中的首个元素进行判断 * * 只有哈希值一致（还说明不了key是否一致），且key也相同（必要时需要用到equals()方法）时， * 这里才认定是存在同位元素（在HashMap中占据相同位置的元素） */ if(p.hash == hash && ((k = p.key) == key || (key != null && key.equals(k)))) { e = p; // 如果该哈希槽上链接的是红黑树结点，则需要调用红黑树的插入方法 } else if(p instanceof TreeNode) { e = ((TreeNode<K, V>) p).putTreeVal(this, tab, hash, key, value); } else { // 遍历哈希槽后面链接的其他元素（binCount统计的是插入新元素之前遍历过的元素数量） for(int binCount = 0; ; ++binCount) { // 如果没有找到同位元素，则需要插入新元素 if((e = p.next) == null) { // 插入一个普通结点 p.next = newNode(hash, key, value, null); // 哈希槽（链）上的元素数量增加到TREEIFY_THRESHOLD后，这些元素进入波动期，即将从链表转换为红黑树 if(binCount >= TREEIFY_THRESHOLD - 1) { // -1 for 1st treeifyBin(tab, hash); } break; } /* * 对哈希槽后面链接的其他元素进行判断 * * 只有哈希值一致（还说明不了key是否一致），且key也相同（必要时需要用到equals()方法）时， * 这里才认定是存在同位元素（在HashMap中占据相同位置的元素） */ if(e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) { break; } p = e; } } // 如果存在同位元素（在HashMap中占据相同位置的元素） if(e != null) { // existing mapping for key // 获取旧元素的值 V oldValue = e.value; // 如果不需要维持原状（可以覆盖旧值），或者旧值为null if(!onlyIfAbsent || oldValue == null) { // 更新旧值 e.value = value; } afterNodeAccess(e); // 返回覆盖前的旧值 return oldValue; } } // HashMap的更改次数加一 ++modCount; // 如果哈希数组的容量已超过阈值，则需要对哈希数组扩容 if(++size>threshold) { // 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组 resize(); } afterNodeInsertion(evict); // 如果插入的是全新的元素，在这里返回null return null; } /** * Initializes or doubles table size. * If null, allocates in accord with initial capacity target held in field threshold. * Otherwise, because we are using power-of-two expansion, * the elements from each bin must either stay at same index, * or move with a power of two offset in the new table. * * @return the table */ /* * 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组 * * 注：哈希数组的容量跟HashMap存放的元素数量没有必然联系 * 哈希数组只存放一系列同位元素（在HashMap中占据相同位置的元素）中最早进来的那个 */ final Node<K, V>[] resize() { Node<K, V>[] oldTab = table; // 旧容量 int oldCap = (oldTab == null) ? 0 : oldTab.length; // 旧阈值 int oldThr = threshold; // 新容量 int newCap; // 新阈值，初始化为0 int newThr = 0; // 如果哈希数组已经初始化（非首次进来） if(oldCap>0) { // 如果哈希表数组容量已经超过最大容量 if(oldCap >= MAXIMUM_CAPACITY) { // 将HashMap的阈值更新为允许的最大值 threshold = Integer.MAX_VALUE; // 不需要更改哈希数组（容量未发生变化），直接返回 return oldTab; } else { // 尝试将哈希表数组容量加倍 newCap = oldCap << 1; // 如果容量成功加倍（没有达到上限），则将阈值也加倍 if(newCap<MAXIMUM_CAPACITY && oldCap >= DEFAULT_INITIAL_CAPACITY) { newThr = oldThr << 1; // double threshold } } // 如果哈希数组还未初始化（首次进来） } else { /* initial capacity was placed in threshold */ // 如果实例化HashMap时已经指定了初始容量，则将哈希数组当前容量初始化为与旧阈值一样大（初始容量与旧阈值的计算关系参见tableSizeFor()方法） if(oldThr>0) { newCap = oldThr; /* zero initial threshold signifies using defaults */ // 如果实例化HashMap时没有指定初始容量，则使用默认的容量与阈值 } else { newCap = DEFAULT_INITIAL_CAPACITY; newThr = (int) (DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY); } } /* * 至此，如果newThr==0，则可能有以下两种情形： * 1.哈希数组已经初始化，且哈希数组的容量还未超出最大容量， * 但是，在执行了加倍操作后，哈希数组的容量达到了上限 * 2.哈希数组还未初始化，但在实例化HashMap时指定了初始容量 */ if(newThr == 0) { float ft = (float) newCap * loadFactor; newThr = newCap<MAXIMUM_CAPACITY && ft<(float) MAXIMUM_CAPACITY ? (int) ft // 针对第二种情况，将阈值更新为初始容量*装载因子 : Integer.MAX_VALUE; // 针对第一种情况，将阈值更新为最大值 } // 更新阈值 threshold = newThr; // 至此，说明哈希数组需要初始化，或者需要扩容，即创建新的哈希数组 @SuppressWarnings({"rawtypes", "unchecked"}) Node<K, V>[] newTab = (Node<K, V>[]) new Node[newCap]; table = newTab; // 如果是扩容，则需要将旧元素复制到新容器 if(oldTab != null) { for(int j = 0; j<oldCap; ++j) { Node<K, V> e = oldTab[j]; // 如果当前哈希槽上存在元素 if(e != null) { // 置空该哈希槽 oldTab[j] = null; // 如果该哈希槽上只有一个元素 if(e.next == null) { // 由于总容量变了，所以需要重新哈希 newTab[e.hash & (newCap - 1)] = e; // 如果该哈希槽上链接了不止一个元素，且该元素是TreeNode类型 } else if(e instanceof TreeNode) { // 拆分红黑树以适应新的容量要求 ((TreeNode<K, V>) e).split(this, newTab, j, oldCap); // 如果该哈希槽上链接了不止一个元素，且该元素是普通Node类型 } else { // preserve order Node<K, V> loHead = null, loTail = null; Node<K, V> hiHead = null, hiTail = null; Node<K, V> next; // 这里跟split()操作类似，将原有的结点分成两拨，以适应新的容量需求 do { next = e.next; if((e.hash & oldCap) == 0) { if(loTail == null) { loHead = e; } else { loTail.next = e; } loTail = e; } else { if(hiTail == null) { hiHead = e; } else { hiTail.next = e; } hiTail = e; } } while((e = next) != null); if(loTail != null) { loTail.next = null; newTab[j] = loHead; } if(hiTail != null) { hiTail.next = null; newTab[j + oldCap] = hiHead; } } } } } return newTab; } /** * Replaces all linked nodes in bin at index for given hash unless * table is too small, in which case resizes instead. */ /* * 观察哈希槽（链）上处于波动期的元素，以决定下一步是扩容还是将链表转换为红黑树 * * tab：待转换的链表 * hash：某元素的哈希值 */ final void treeifyBin(Node<K, V>[] tab, int hash) { int n; // 哈希数组的容量还未达到形成一棵红黑树的最低要求 if(tab == null || (n = tab.length)<MIN_TREEIFY_CAPACITY) { // 初始化哈希数组，或者对哈希数组扩容，返回新的哈希数组 resize(); // 满足从链表转换为红黑树的要求 } else { // 计算哈希槽索引 int index = (n - 1) & hash; Node<K, V> e = tab[index]; if(e!= null) { TreeNode<K, V> hd = null, tl = null; do { // 将元素e从链表结点转换为红黑树结点 TreeNode<K, V> p = replacementTreeNode(e, null); if(tl == null) { hd = p; } else { p.prev = tl; tl.next = p; } tl = p; } while((e = e.next) != null); if((tab[index] = hd) != null) { // 遍历hd链表上的所有元素，创建一棵红黑树 hd.treeify(tab); } } } } /* These methods are also used when serializing HashSets */ // 获取HashMap当前使用的装载因子 final float loadFactor() { return loadFactor; } // 获取哈希数组的容量 final int capacity() { return (table != null) ? table.length : (threshold>0) ? threshold : DEFAULT_INITIAL_CAPACITY; } /** * Implements Map.remove and related methods. * * @param hash hash for key * @param key the key * @param value the value to match if matchValue, else ignored * @param matchValue if true only remove if value is equal * @param movable if false do not move other nodes while removing * * @return the node, or null if none */ /* * 从HashMap中移除指定的元素，并返回刚刚移除的元素（移除失败返回null） * * matchValue 移除元素时是否需要考虑value的匹配问题 * movable 移除元素后如果红黑树根结点发生了变化，那么是否需要改变结点在链表上的顺序 */ final Node<K, V> removeNode(int hash, Object key, Object value, boolean matchValue, boolean movable) { Node<K, V>[] tab; Node<K, V> p; int n, index; if((tab = table) != null && (n = tab.length)>0 && (p = tab[index = (n - 1) & hash]) != null) { Node<K, V> node = null, e; K k; V v; /* 根据给定的key和hash（由key计算而来）查找对应的（同位）元素 */ if(p.hash == hash && ((k = p.key) == key || (key != null && key.equals(k)))) { node = p; } else if((e = p.next) != null) { if(p instanceof TreeNode) { node = ((TreeNode<K, V>) p).getTreeNode(hash, key); } else { do { if(e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) { node = e; break; } p = e; } while((e = e.next) != null); } } /* * 从HashMap中移除匹配的元素 * 可能只需要匹配hash和key就行，也可能还要匹配value，这取决于matchValue参数 */ if(node != null && (!matchValue || (v = node.value) == value || (value != null && value.equals(v)))) { if(node instanceof TreeNode) { ((TreeNode<K, V>) node).removeTreeNode(this, tab, movable); } else if(node == p) { tab[index] = node.next; } else { p.next = node.next; } ++modCount; --size; afterNodeRemoval(node); return node; } } return null; } /** * Basic hash bin node, used for most entries. (See below for * TreeNode subclass, and in LinkedHashMap for its Entry subclass.) */ // HashMap中的普通结点信息，每个Node代表一个元素，里面包含了key和value的信息 static class Node<K, V> implements Map.Entry<K, V> { final int hash; final K key; V value; Node<K, V> next; Node(int hash, K key, V value, Node<K, V> next) { this.hash = hash; this.key = key; this.value = value; this.next = next; } public final K getKey() { return key; } public final V getValue() { return value; } public final V setValue(V newValue) { V oldValue = value; value = newValue; return oldValue; } public final String toString() { return key + "=" + value; } public final int hashCode() { return Objects.hashCode(key) ^ Objects.hashCode(value); } public final boolean equals(Object o) { if(o == this) { return true; } if(o instanceof Map.Entry) { Map.Entry<?, ?> e = (Map.Entry<?, ?>) o; return Objects.equals(key, e.getKey()) && Objects.equals(value, e.getValue()); } return false; } } /** * Entry for Tree bins. Extends LinkedHashMap.Entry (which in turn * extends Node) so can be used as extension of either regular or * linked node. */ // HashMap中的红黑树结点 static final class TreeNode<K,V> extends LinkedHashMap.Entry<K,V> { TreeNode<K,V> parent; // red-black tree links TreeNode<K,V> left; TreeNode<K,V> right; boolean red; TreeNode<K,V> prev; // needed to unlink next upon deletion // 仍然需要维护next链接 TreeNode(int hash, K key, V val, Node<K, V> next) { super(hash, key, val, next); } /*▼ 创建/反创建 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┓ */ /** * Forms tree of the nodes linked from this node. */ /* * 遍历当前TreeNode链表上的所有元素，创建一棵红黑树 * * 创建完成后，当前的TreeNode元素以及后面链接的那串元素具有链表与红黑树两种结构 * 其中，链表是靠着结点的prev和next来链接的 * 除此之外，由于创建红黑树的过程中，根结点可能会发生动态变化， * 所以，在红黑树创建完成后，当前的TreeNode元素可能是，也可能不是红黑树的根结点， * 如果当前的TreeNode元素不是红黑树的根结点，那么它在原来链表上的相对位置也会发生变化（通过moveRootToFront()方法调整） */ final void treeify(Node<K, V>[] tab) { TreeNode<K, V> root = null; // 遍历待插入元素 for(TreeNode<K, V> x = this, next; x != null; x = next) { next = (TreeNode<K, V>) x.next; x.left = x.right = null; // 创建根结点 if(root == null) { x.parent = null; // 根结点parent为null x.red = false; // 根结点为黑色 root = x; // root指向根结点 } else { K k = x.key; int h = x.hash; Class<?> kc = null; // 遍历红黑树，将k所代表的元素插入到红黑树中合适的位置 for(TreeNode<K, V> p = root; ; ) { int dir, ph; K pk = p.key; /* * 判断待插入元素的插入位置，是向左查找？还是向右查找？ * 判断依据依次为： * ┌──不相同，可以得出结果 ★ * ┌──不相同，直接得出结果 ★ ┌──类型一致───使用compareTo()方法判断──┤ * 判断hash ──┤ ┌──有效───检查参与比较的元素类型──┤ └───相同───┐ * └──相同───检查Comparable接口──┤ └───类型不一致───────────────────────────────────┼──调用tieBreakOrder()方法，可以得出结果 ★ * └───无效──────────────────────────────────────────────────────────────────────┘ * * */ // 待插入结点的hash值较小，则向左搜寻合适的插入位置 if((ph = p.hash)>h) { dir = -1; // 待插入结点的hash值较大，则向右搜寻合适的插入位置 } else if(ph<h) { dir = 1; // 待插入结点的hash值出现了雷同 } else if((kc == null && (kc = comparableClassFor(k)) == null) // 如果k（的类类型）没有实现“有效”的Comparable接口 || (dir = compareComparables(kc, k, pk)) == 0) { // 或者，待插入元素与已存在元素类型不同，无法比较 // 终极判等方式：使用对象的类名和对象本身的哈希码去比较两个对象的大小，而且返回值一定是-1或者是1 dir = tieBreakOrder(k, pk); } // 向指定的位置插入结点 TreeNode<K, V> xp = p; if((p = (dir<=0) ? p.left : p.right) == null) { x.parent = xp; if(dir<=0) { xp.left = x; } else { xp.right = x; } // 将元素x插入到红黑树root后，可能会破坏其平衡性，所以这里需要做出调整，保持红黑树的平衡 root = balanceInsertion(root, x); break; } } } } /* * 由于红黑树根结点可能发生了变化，所以需要检查/调整链表顺序： * 将root放入哈希数组tab的合适位置，且将root指向的元素移动到链表的头部 */ moveRootToFront(tab, root); } /** * Returns a list of non-TreeNodes replacing those linked from this node. */ // 遍历当前TreeNode红黑树上所有元素，创建一个链表 final Node<K, V> untreeify(HashMap<K, V> map) { Node<K, V> hd = null, tl = null; for(Node<K, V> q = this; q != null; q = q.next) { Node<K, V> p = map.replacementNode(q, null); if(tl == null) { hd = p; } else { tl.next = p; } tl = p; } return hd; } /*▲ 创建/反创建 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┛ */ /*▼ 插入/删除 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┓ */ /** * Tree version of putVal. */ // 向当前红黑树中插入元素 final TreeNode<K, V> putTreeVal(HashMap<K, V> map, Node<K, V>[] tab, int h, K k, V v) { Class<?> kc = null; boolean searched = false; // 获取当前红黑树的根结点 TreeNode<K, V> root = (parent != null) ? root() : this; for(TreeNode<K, V> p = root; ; ) { int dir, ph; K pk; if((ph = p.hash)>h) { dir = -1; } else if(ph<h) { dir = 1; } else if((pk = p.key) == k || (k != null && k.equals(pk))) { return p; } else if((kc == null && (kc = comparableClassFor(k)) == null) || (dir = compareComparables(kc, k, pk)) == 0) { if(!searched) { TreeNode<K, V> q, ch; searched = true; if(((ch = p.left) != null && (q = ch.find(h, k, kc)) != null) || ((ch = p.right) != null && (q = ch.find(h, k, kc)) != null)) { return q; } } // 终极判等方式：使用对象的类名和对象本身的哈希码去比较两个对象的大小，而且返回值一定是-1或者是1 dir = tieBreakOrder(k, pk); } TreeNode<K, V> xp = p; if((p = (dir<=0) ? p.left : p.right) == null) { Node<K, V> xpn = xp.next; TreeNode<K, V> x = map.newTreeNode(h, k, v, xpn); if(dir<=0) { xp.left = x; } else { xp.right = x; } xp.next = x; x.parent = x.prev = xp; if(xpn != null) { ((TreeNode<K, V>) xpn).prev = x; } // 将元素x插入到红黑树root后，可能会破坏其平衡性，所以这里需要做出调整，保持红黑树的平衡 TreeNode<K, V> r = balanceInsertion(root, x); /* * 由于红黑树根结点可能发生了变化，所以需要检查/调整链表顺序： * 将r放入哈希数组tab的合适位置，且将r指向的元素移动到链表的头部 */ moveRootToFront(tab, r); return null; } } } /** * Removes the given node, that must be present before this call. * This is messier than typical red-black deletion code because we * cannot swap the contents of an interior node with a leaf * successor that is pinned by "next" pointers that are accessible * independently during traversal. So instead we swap the tree * linkages. If the current tree appears to have too few nodes, * the bin is converted back to a plain bin. (The test triggers * somewhere between 2 and 6 nodes, depending on tree structure). */ // 将元素从红黑树中移除 final void removeTreeNode(HashMap<K, V> map, Node<K, V>[] tab, boolean movable) { int n; if(tab == null || (n = tab.length) == 0) { return; } int index = (n - 1) & hash; TreeNode<K, V> first = (TreeNode<K, V>) tab[index], root = first, rl; TreeNode<K, V> succ = (TreeNode<K, V>) next, pred = prev; if(pred == null) { tab[index] = first = succ; } else { pred.next = succ; } if(succ != null) { succ.prev = pred; } if(first == null) { return; } if(root.parent != null) { // 获取当前红黑树的根结点 root = root.root(); } if(root == null || (movable && (root.right == null || (rl = root.left) == null || rl.left == null))) { // 遍历红黑树first上所有元素，创建一个链表 tab[index] = first.untreeify(map); // too small return; } TreeNode<K, V> p = this, pl = left, pr = right, replacement; if(pl != null && pr != null) { TreeNode<K, V> s = pr, sl; // find successor while((sl = s.left) != null) { s = sl; } boolean c = s.red; s.red = p.red; p.red = c; // swap colors TreeNode<K, V> sr = s.right; TreeNode<K, V> pp = p.parent; if(s == pr) { // p was s's direct parent p.parent = s; s.right = p; } else { TreeNode<K, V> sp = s.parent; if((p.parent = sp) != null) { if(s == sp.left) { sp.left = p; } else { sp.right = p; } } if((s.right = pr) != null) { pr.parent = s; } } p.left = null; if((p.right = sr) != null) { sr.parent = p; } if((s.left = pl) != null) { pl.parent = s; } if((s.parent = pp) == null) { root = s; } else if(p == pp.left) { pp.left = s; } else { pp.right = s; } if(sr != null) { replacement = sr; } else { replacement = p; } } else if(pl != null) { replacement = pl; } else if(pr != null) { replacement = pr; } else { replacement = p; } if(replacement != p) { TreeNode<K, V> pp = replacement.parent = p.parent; if(pp == null) { root = replacement; } else if(p == pp.left) { pp.left = replacement; } else { pp.right = replacement; } p.left = p.right = p.parent = null; } TreeNode<K, V> r = p.red ? root : balanceDeletion(root, replacement); // 将元素x从红黑树root移除后，可能会破坏其平衡性，所以这里需要做出调整，保持红黑树的平衡 if(replacement == p) { // detach TreeNode<K, V> pp = p.parent; p.parent = null; if(pp != null) { if(p == pp.left) { pp.left = null; } else if(p == pp.right) { pp.right = null; } } } if(movable) { /* * 由于红黑树根结点可能发生了变化，所以需要检查/调整链表顺序： * 将r放入哈希数组tab的合适位置，且将r指向的元素移动到链表的头部 */ moveRootToFront(tab, r); } } // 将元素x插入到红黑树root后，可能会破坏其平衡性，所以这里需要做出调整，保持红黑树的平衡 static <K, V> TreeNode<K, V> balanceInsertion(TreeNode<K, V> root, TreeNode<K, V> x) { // 新插入的结点一律先设置为红色 x.red = true; for(TreeNode<K, V> xp, xpp, xppl, xppr; ; ) { if((xp = x.parent) == null) { x.red = false; return x; } if(!xp.red || (xpp = xp.parent) == null) { return root; } if(xp == (xppl = xpp.left)) { if((xppr = xpp.right) != null && xppr.red) { xppr.red = false; xp.red = false; xpp.red = true; x = xpp; } else { if(x == xp.right) { root = rotateLeft(root, x = xp); xpp = (xp = x.parent) == null ? null : xp.parent; } if(xp != null) { xp.red = false; if(xpp != null) { xpp.red = true; root = rotateRight(root, xpp); } } } } else { if(xppl != null && xppl.red) { xppl.red = false; xp.red = false; xpp.red = true; x = xpp; } else { if(x == xp.left) { root = rotateRight(root, x = xp); xpp = (xp = x.parent) == null ? null : xp.parent; } if(xp != null) { xp.red = false; if(xpp != null) { xpp.red = true; root = rotateLeft(root, xpp); } } } } } } // 将元素x从红黑树root移除后，可能会破坏其平衡性，所以这里需要做出调整，保持红黑树的平衡 static <K, V> TreeNode<K, V> balanceDeletion(TreeNode<K, V> root, TreeNode<K, V> x) { for(TreeNode<K, V> xp, xpl, xpr; ; ) { if(x == null || x == root) { return root; } else if((xp = x.parent) == null) { x.red = false; return x; } else if(x.red) { x.red = false; return root; } else if((xpl = xp.left) == x) { if((xpr = xp.right) != null && xpr.red) { xpr.red = false; xp.red = true; root = rotateLeft(root, xp); xpr = (xp = x.parent) == null ? null : xp.right; } if(xpr == null) { x = xp; } else { TreeNode<K, V> sl = xpr.left, sr = xpr.right; if((sr == null || !sr.red) && (sl == null || !sl.red)) { xpr.red = true; x = xp; } else { if(sr == null || !sr.red) { if(sl != null) { sl.red = false; } xpr.red = true; root = rotateRight(root, xpr); xpr = (xp = x.parent) == null ? null : xp.right; } if(xpr != null) { xpr.red = (xp != null) && xp.red; if((sr = xpr.right) != null) { sr.red = false; } } if(xp != null) { xp.red = false; root = rotateLeft(root, xp); } x = root; } } } else { // symmetric if(xpl != null && xpl.red) { xpl.red = false; xp.red = true; root = rotateRight(root, xp); xpl = (xp = x.parent) == null ? null : xp.left; } if(xpl == null) { x = xp; } else { TreeNode<K, V> sl = xpl.left, sr = xpl.right; if((sl == null || !sl.red) && (sr == null || !sr.red)) { xpl.red = true; x = xp; } else { if(sl == null || !sl.red) { if(sr != null) { sr.red = false; } xpl.red = true; root = rotateLeft(root, xpl); xpl = (xp = x.parent) == null ? null : xp.left; } if(xpl != null) { xpl.red = (xp != null) && xp.red; if((sl = xpl.left) != null) { sl.red = false; } } if(xp != null) { xp.red = false; root = rotateRight(root, xp); } x = root; } } } } } // 左旋 static <K, V> TreeNode<K, V> rotateLeft(TreeNode<K, V> root, TreeNode<K, V> p) { TreeNode<K, V> r, pp, rl; if(p != null && (r = p.right) != null) { if((rl = p.right = r.left) != null) { rl.parent = p; } if((pp = r.parent = p.parent) == null) { (root = r).red = false; } else if(pp.left == p) { pp.left = r; } else { pp.right = r; } r.left = p; p.parent = r; } return root; } // 右旋 static <K, V> TreeNode<K, V> rotateRight(TreeNode<K, V> root, TreeNode<K, V> p) { TreeNode<K, V> l, pp, lr; if(p != null && (l = p.left) != null) { if((lr = p.left = l.right) != null) { lr.parent = p; } if((pp = l.parent = p.parent) == null) { (root = l).red = false; } else if(pp.right == p) { pp.right = l; } else { pp.left = l; } l.right = p; p.parent = l; } return root; } /*▲ 插入/删除 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┛ */ /** * Ensures that the given root is the first node of its bin. */ /* * 在红黑树根结点可能发生变化时，需要检查/调整链表顺序： * 将root放入哈希数组tab的合适位置，且将root指向的元素移动到链表的头部 */ static <K, V> void moveRootToFront(Node<K, V>[] tab, TreeNode<K, V> root) { int n; if(root != null && tab != null && (n = tab.length)>0) { int index = (n - 1) & root.hash; TreeNode<K, V> first = (TreeNode<K, V>) tab[index]; if(root != first) { tab[index] = root; TreeNode<K, V> rp = root.prev; Node<K, V> rn = root.next; if(rn != null) { ((TreeNode<K, V>) rn).prev = rp; } if(rp != null) { rp.next = rn; } if(first != null) { first.prev = root; } root.next = first; root.prev = null; } assert checkInvariants(root); } } /** * Tie-breaking utility for ordering insertions when equal * hashCodes and non-comparable. We don't require a total * order, just a consistent insertion rule to maintain * equivalence across rebalancings. Tie-breaking further than * necessary simplifies testing a bit. */ // 终极判等方式：使用对象的类名和对象本身的哈希码去比较两个对象的大小，而且返回值一定是-1或者是1 static int tieBreakOrder(Object a, Object b) { int d; if(a == null || b == null || (d = a.getClass().getName().compareTo(b.getClass().getName())) == 0) { d = (System.identityHashCode(a)<=System.identityHashCode(b) ? -1 : 1); } return d; } /** * Returns root of tree containing this node. */ // 获取当前红黑树的根结点 final TreeNode<K, V> root() { for(TreeNode<K, V> r = this, p; ; ) { if((p = r.parent) == null) { return r; } r = p; } } /** * Finds the node starting at root p with the given hash and key. * The kc argument caches comparableClassFor(key) upon first use * comparing keys. */ // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null final TreeNode<K, V> find(int hash, Object key, Class<?> kc) { TreeNode<K, V> p = this; do { int ph, dir; K pk; TreeNode<K, V> pl = p.left, pr = p.right, q; if((ph = p.hash)>hash) { p = pl; } else if(ph<hash) { p = pr; } else if((pk = p.key) == key || (key != null && key.equals(pk))) { return p; } else if(pl == null) { p = pr; } else if(pr == null) { p = pl; } else if((kc != null || (kc = comparableClassFor(key)) != null) && (dir = compareComparables(kc, key, pk)) != 0) { p = (dir<0) ? pl : pr; } else if((q = pr.find(hash, key, kc)) != null) { return q; } else { p = pl; } } while(p != null); return null; } /** * Calls find for root node. */ // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null final TreeNode<K, V> getTreeNode(int hash, Object key) { return ((parent != null) ? root() : this).find(hash, key, null); } /** * Splits nodes in a tree bin into lower and upper tree bins, * or untreeifies if now too small. Called only from resize; * see above discussion about split bits and indices. * * @param map the map * @param tab the table for recording bin heads * @param index the index of the table being split * @param bit the bit of hash to split on */ // 拆分红黑树以适应新的容量要求，因为扩容会导致index哈希槽处的那些元素进行再哈希，并最多分成两拨（bit为2的冪，一般传入的值是哈希数组旧容量） final void split(HashMap<K, V> map, Node<K, V>[] tab, int index, int bit) { TreeNode<K, V> b = this; // Relink into lo and hi lists, preserving order TreeNode<K, V> loHead = null, loTail = null; TreeNode<K, V> hiHead = null, hiTail = null; int lc = 0, hc = 0; for(TreeNode<K, V> e = b, next; e != null; e = next) { next = (TreeNode<K, V>) e.next; e.next = null; // 扩容后，元素e的位置不会改变（低区间） if((e.hash & bit) == 0) { if((e.prev = loTail) == null) { loHead = e; } else { loTail.next = e; } loTail = e; ++lc; // 扩容后，元素e会进入新的位置（高区间） } else { if((e.prev = hiTail) == null) { hiHead = e; } else { hiTail.next = e; } hiTail = e; ++hc; } } if(loHead != null) { if(lc<=UNTREEIFY_THRESHOLD) { // 遍历红黑树loHead上所有元素，创建一个链表 tab[index] = loHead.untreeify(map); } else { tab[index] = loHead; if(hiHead != null) { // 遍历loHead链表上的所有元素，创建一棵红黑树 loHead.treeify(tab); } // (else is already treeified) } } if(hiHead != null) { if(hc<=UNTREEIFY_THRESHOLD) { // 遍历红黑树hiHead上所有元素，创建一个链表 tab[index + bit] = hiHead.untreeify(map); } else { tab[index + bit] = hiHead; if(loHead != null) { // 遍历hiHead链表上的所有元素，创建一棵红黑树 hiHead.treeify(tab); } } } } /** * Recursive invariant check */ static <K, V> boolean checkInvariants(TreeNode<K, V> t) { TreeNode<K, V> tp = t.parent, tl = t.left, tr = t.right, tb = t.prev, tn = (TreeNode<K, V>) t.next; if(tb != null && tb.next != t) { return false; } if(tn != null && tn.prev != t) { return false; } if(tp != null && t != tp.left && t != tp.right) { return false; } if(tl != null && (tl.parent != t || tl.hash>t.hash)) { return false; } if(tr != null && (tr.parent != t || tr.hash<t.hash)) { return false; } if(t.red && tl != null && tl.red && tr != null && tr.red) { return false; } if(tl != null && !checkInvariants(tl)) { return false; } return tr == null || checkInvariants(tr); } } // HashMap中key的集合 final class KeySet extends AbstractSet<K> { public final int size() { return size; } public final boolean remove(Object key) { return removeNode(hash(key), key, null, false, true) != null; } public final void clear() { HashMap.this.clear(); } public final boolean contains(Object o) { return containsKey(o); } public final Iterator<K> iterator() { return new KeyIterator(); } public final Spliterator<K> spliterator() { return new KeySpliterator<>(HashMap.this, 0, -1, 0, 0); } public final void forEach(Consumer<? super K> action) { Node<K, V>[] tab; if(action == null) { throw new NullPointerException(); } if(size>0 && (tab = table) != null) { int mc = modCount; for(Node<K, V> e : tab) { for(; e != null; e = e.next) { action.accept(e.key); } } if(modCount != mc) { throw new ConcurrentModificationException(); } } } } // HashMap中value的集合 final class Values extends AbstractCollection<V> { public final int size() { return size; } public final void clear() { HashMap.this.clear(); } public final boolean contains(Object o) { return containsValue(o); } public final Iterator<V> iterator() { return new ValueIterator(); } public final Spliterator<V> spliterator() { return new ValueSpliterator<>(HashMap.this, 0, -1, 0, 0); } public final void forEach(Consumer<? super V> action) { Node<K, V>[] tab; if(action == null) { throw new NullPointerException(); } if(size>0 && (tab = table) != null) { int mc = modCount; for(Node<K, V> e : tab) { for(; e != null; e = e.next) action.accept(e.value); } if(modCount != mc) { throw new ConcurrentModificationException(); } } } } // HashMap中key-value的集合，Entry的本质就是Node final class EntrySet extends AbstractSet<Map.Entry<K, V>> { public final int size() { return size; } public final void clear() { HashMap.this.clear(); } public final boolean contains(Object o) { if(!(o instanceof Map.Entry)) { return false; } Map.Entry<?, ?> e = (Map.Entry<?, ?>) o; Object key = e.getKey(); // 根据给定的key和hash（由key计算而来）查找对应的（同位）元素，如果找不到，则返回null Node<K, V> candidate = getNode(hash(key), key); return candidate != null && candidate.equals(e); } public final boolean remove(Object o) { if(o instanceof Map.Entry) { Map.Entry<?, ?> e = (Map.Entry<?, ?>) o; Object key = e.getKey(); Object value = e.getValue(); return removeNode(hash(key), key, value, true, true) != null; } return false; } public final Iterator<Map.Entry<K, V>> iterator() { return new EntryIterator(); } public final Spliterator<Map.Entry<K, V>> spliterator() { return new EntrySpliterator<>(HashMap.this, 0, -1, 0, 0); } public final void forEach(Consumer<? super Map.Entry<K, V>> action) { Node<K, V>[] tab; if(action == null) { throw new NullPointerException(); } if(size>0 && (tab = table) != null) { int mc = modCount; for(Node<K, V> e : tab) { for(; e != null; e = e.next) action.accept(e); } if(modCount != mc) { throw new ConcurrentModificationException(); } } } } // HashMap迭代器 abstract class HashIterator { // 当前正在处理元素 Node<K, V> next; // next entry to return // 下次即将即将处理的元素 Node<K, V> current; // current entry // 记录HashMap当前的修改次数，后续遍历时如果发现修改次数发生了变化，则返回失败信息 int expectedModCount; // for fast-fail // 下一个待处理元素所在的哈希槽索引 int index; // current slot HashIterator() { expectedModCount = modCount; Node<K, V>[] t = table; current = next = null; index = 0; if(t != null && size>0) { // advance to first entry do { } while(index<t.length && (next = t[index++]) == null); } } public final boolean hasNext() { return next != null; } final Node<K, V> nextNode() { Node<K, V>[] t; Node<K, V> e = next; if(modCount != expectedModCount) { throw new ConcurrentModificationException(); } if(e == null) { throw new NoSuchElementException(); } if((next = (current = e).next) == null && (t = table) != null) { do { } while(index<t.length && (next = t[index++]) == null); } return e; } public final void remove() { Node<K, V> p = current; if(p == null) { throw new IllegalStateException(); } if(modCount != expectedModCount) { throw new ConcurrentModificationException(); } current = null; removeNode(p.hash, p.key, null, false, false); expectedModCount = modCount; } } // key的迭代器 final class KeyIterator extends HashIterator implements Iterator<K> { public final K next() { return nextNode().key; } } // value的迭代器 final class ValueIterator extends HashIterator implements Iterator<V> { public final V next() { return nextNode().value; } } // key-value对的迭代器 final class EntryIterator extends HashIterator implements Iterator<Map.Entry<K, V>> { public final Map.Entry<K, V> next() { return nextNode(); } } // HashMap的可分割迭代器 static class HashMapSpliterator<K, V> { final HashMap<K, V> map; Node<K, V> current; // current node int index; // current index, modified on advance/split int fence; // one past last index int est; // size estimate int expectedModCount; // for comodification checks HashMapSpliterator(HashMap<K, V> m, int origin, int fence, int est, int expectedModCount) { this.map = m; this.index = origin; this.fence = fence; this.est = est; this.expectedModCount = expectedModCount; } public final long estimateSize() { getFence(); // force init return (long) est; } // initialize fence and size on first use final int getFence() { int hi; if((hi = fence)<0) { HashMap<K, V> m = map; est = m.size; expectedModCount = m.modCount; Node<K, V>[] tab = m.table; hi = fence = (tab == null) ? 0 : tab.length; } return hi; } } // key的可分割迭代器 static final class KeySpliterator<K, V> extends HashMapSpliterator<K, V> implements Spliterator<K> { KeySpliterator(HashMap<K, V> m, int origin, int fence, int est, int expectedModCount) { super(m, origin, fence, est, expectedModCount); } // 从容器的指定范围切割一段元素，将其打包到Spliterator后返回，特征值不变（这里会切割前一半元素出来） public KeySpliterator<K, V> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; return (lo >= mid || current != null) ? null : new KeySpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount); } // 对容器中的单个当前元素执行择取操作 public boolean tryAdvance(Consumer<? super K> action) { int hi; if(action == null) { throw new NullPointerException(); } Node<K, V>[] tab = map.table; if(tab != null && tab.length >= (hi = getFence()) && index >= 0) { while(current != null || index<hi) { if(current == null) { current = tab[index++]; } else { K k = current.key; current = current.next; action.accept(k); if(map.modCount != expectedModCount) { throw new ConcurrentModificationException(); } return true; } } } return false; } // 遍历容器内每个元素，在其上执行相应的择取操作 public void forEachRemaining(Consumer<? super K> action) { int i, hi, mc; if(action == null) { throw new NullPointerException(); } HashMap<K, V> m = map; Node<K, V>[] tab = m.table; if((hi = fence)<0) { mc = expectedModCount = m.modCount; hi = fence = (tab == null) ? 0 : tab.length; } else { mc = expectedModCount; } if(tab != null && tab.length >= hi && (i = index) >= 0 && (i<(index = hi) || current != null)) { Node<K, V> p = current; current = null; do { if(p == null) p = tab[i++]; else { action.accept(p.key); p = p.next; } } while(p != null || i<hi); if(m.modCount != mc) { throw new ConcurrentModificationException(); } } } public int characteristics() { return (fence<0 || est == map.size ? Spliterator.SIZED : 0) | Spliterator.DISTINCT; } } // value的可分割迭代器 static final class ValueSpliterator<K, V> extends HashMapSpliterator<K, V> implements Spliterator<V> { ValueSpliterator(HashMap<K, V> m, int origin, int fence, int est, int expectedModCount) { super(m, origin, fence, est, expectedModCount); } // 从容器的指定范围切割一段元素，将其打包到Spliterator后返回，特征值不变（这里会切割前一半元素出来） public ValueSpliterator<K, V> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; return (lo >= mid || current != null) ? null : new ValueSpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount); } // 对容器中的单个当前元素执行择取操作 public boolean tryAdvance(Consumer<? super V> action) { int hi; if(action == null) { throw new NullPointerException(); } Node<K, V>[] tab = map.table; if(tab != null && tab.length >= (hi = getFence()) && index >= 0) { while(current != null || index<hi) { if(current == null) { current = tab[index++]; } else { V v = current.value; current = current.next; action.accept(v); if(map.modCount != expectedModCount) { throw new ConcurrentModificationException(); } return true; } } } return false; } // 遍历容器内每个元素，在其上执行相应的择取操作 public void forEachRemaining(Consumer<? super V> action) { int i, hi, mc; if(action == null) { throw new NullPointerException(); } HashMap<K, V> m = map; Node<K, V>[] tab = m.table; if((hi = fence)<0) { mc = expectedModCount = m.modCount; hi = fence = (tab == null) ? 0 : tab.length; } else { mc = expectedModCount; } if(tab != null && tab.length >= hi && (i = index) >= 0 && (i<(index = hi) || current != null)) { Node<K, V> p = current; current = null; do { if(p == null) p = tab[i++]; else { action.accept(p.value); p = p.next; } } while(p != null || i<hi); if(m.modCount != mc) { throw new ConcurrentModificationException(); } } } public int characteristics() { return (fence<0 || est == map.size ? Spliterator.SIZED : 0); } } // key-value的可分割迭代器 static final class EntrySpliterator<K, V> extends HashMapSpliterator<K, V> implements Spliterator<Map.Entry<K, V>> { EntrySpliterator(HashMap<K, V> m, int origin, int fence, int est, int expectedModCount) { super(m, origin, fence, est, expectedModCount); } // 从容器的指定范围切割一段元素，将其打包到Spliterator后返回，特征值不变（这里会切割前一半元素出来） public EntrySpliterator<K, V> trySplit() { int hi = getFence(), lo = index, mid = (lo + hi) >>> 1; return (lo >= mid || current != null) ? null : new EntrySpliterator<>(map, lo, index = mid, est >>>= 1, expectedModCount); } // 对容器中的单个当前元素执行择取操作 public boolean tryAdvance(Consumer<? super Map.Entry<K, V>> action) { int hi; if(action == null) { throw new NullPointerException(); } Node<K, V>[] tab = map.table; if(tab != null && tab.length >= (hi = getFence()) && index >= 0) { while(current != null || index<hi) { if(current == null) { current = tab[index++]; } else { Node<K, V> e = current; current = current.next; action.accept(e); if(map.modCount != expectedModCount) { throw new ConcurrentModificationException(); } return true; } } } return false; } // 遍历容器内每个元素，在其上执行相应的择取操作 public void forEachRemaining(Consumer<? super Map.Entry<K, V>> action) { int i, hi, mc; if(action == null) { throw new NullPointerException(); } HashMap<K, V> m = map; Node<K, V>[] tab = m.table; if((hi = fence)<0) { mc = expectedModCount = m.modCount; hi = fence = (tab == null) ? 0 : tab.length; } else { mc = expectedModCount; } if(tab != null && tab.length >= hi && (i = index) >= 0 && (i<(index = hi) || current != null)) { Node<K, V> p = current; current = null; do { if(p == null) p = tab[i++]; else { action.accept(p); p = p.next; } } while(p != null || i<hi); if(m.modCount != mc) { throw new ConcurrentModificationException(); } } } public int characteristics() { return (fence<0 || est == map.size ? Spliterator.SIZED : 0) | Spliterator.DISTINCT; } } }
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