一，HashTable
哈希表，它相比于hashMap构造简略点，它没有波及红黑树，间接应用链表的形式解决哈希抵触。
咱们看它的字段，和hashMap差不多，应用table寄存元素
private transient Entry<?,?>[] table;private transient int count;private int threshold;private float loadFactor;private transient int modCount = 0;它没有常量字段，默认值是在构造方法外面间接体现的，咱们看一下无参结构：
public Hashtable() { this(11, 0.75f);}1.get()办法
依据key取得value
public synchronized V get(Object key) { Entry<?,?> tab[] = table;//计算下标 int hash = key.hashCode(); int index = (hash & 0x7FFFFFFF) % tab.length;//遍历查找，e=e.next for (Entry<?,?> e = tab[index] ; e != null ; e = e.next) { if ((e.hash == hash) && e.key.equals(key)) { return (V)e.value; } } return null;}2.put()办法
与get()办法相似，也是遍历table，而后调用addEntry()实现增加。
public synchronized V put(K key, V value) { if (value == null) { throw new NullPointerException(); } Entry<?,?> tab[] = table; int hash = key.hashCode(); int index = (hash & 0x7FFFFFFF) % tab.length; @SuppressWarnings("unchecked") Entry<K,V> entry = (Entry<K,V>)tab[index];//如果曾经存在，则笼罩，返回老的值 for(; entry != null ; entry = entry.next) { if ((entry.hash == hash) && entry.key.equals(key)) { V old = entry.value; entry.value = value; return old; } }//不存在，间接增加 addEntry(hash, key, value, index); return null;}addEntry()
private void addEntry(int hash, K key, V value, int index) { modCount++; Entry<?,?> tab[] = table; if (count >= threshold) { //大小超过阈值，要扩容 // Rehash the table if the threshold is exceeded rehash(); tab = table; hash = key.hashCode(); index = (hash & 0x7FFFFFFF) % tab.length; }//增加 @SuppressWarnings("unchecked") Entry<K,V> e = (Entry<K,V>) tab[index]; tab[index] = new Entry<>(hash, key, value, e); count++;}留神这里的手法，间接将新来的节点，放到头部，这样就能够不论前面是否存在节点，都不会呈现问题
protected Entry(int hash, K key, V value, Entry<K,V> next) { this.hash = hash; this.key = key; this.value = value; this.next = next;}二，HashMap
1.常量字段介绍
static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // aka 16 2的四次方，初始化默认的容量static final int MAXIMUM_CAPACITY = 1 << 30; 最大的容量值static final float DEFAULT_LOAD_FACTOR = 0.75f; //容量 负载因子，static final int TREEIFY_THRESHOLD = 8; //链表转换为数的阈值static final int UNTREEIFY_THRESHOLD = 6; //树转坏为链表的阈值static final int MIN_TREEIFY_CAPACITY = 64; //桶中的数据采纳红黑树存储时，整个table的最小容量字段：
transient Node<K,V>[] table; //存储骨干，节点数组transient Set<Map.Entry<K,V>> entrySet;transient int size; //元素数量transient int modCount; //批改次数//The next size value at which to resize (capacity * load factor).int threshold; //下一次扩容的大小，final float loadFactor; //负载因子2.构造函数
2.1罕用的无参结构：
默认构造方法，就间接给负载因子赋值，其余没有操作，其余字段都是默认的。
// Constructs an empty <tt>HashMap</tt> with the default initial // capacity (16) and the default load factor (0.75).public HashMap() { this.loadFactor = DEFAULT_LOAD_FACTOR; // all other fields defaulted}2.2带初始化容器大小，和负载因子的构造方法：
首先要判断传入参数的正确性，而后赋值。
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); this.loadFactor = loadFactor; this.threshold = tableSizeFor(initialCapacity);}2.3带汇合的构造方法：
传入一个Map汇合，调用put办法进行初始化。
public HashMap(Map<? extends K, ? extends V> m) { this.loadFactor = DEFAULT_LOAD_FACTOR; putMapEntries(m, false);}从下面的代码中能够看到，在构造方法中并没有初始化table，具体的table初始化是在put操作上进行的。
3.增加
3.1 put()
是一个入口办法，理论调用的是putVal()办法，其中通过hash()办法计算了key对应的 值
public V put(K key, V value) { return putVal(hash(key), key, value, false, true);}//异或运算，保障存储地位尽量均匀分布。static final int hash(Object key) { int h; return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);}具体的putVal()办法，内容很长
final V putVal(int hash, K key, V value, boolean onlyIfAbsent, boolean evict) { Node<K,V>[] tab; Node<K,V> p; int n, i; //变量初始化，n示意table的长度 if ((tab = table) == null || (n = tab.length) == 0) //容器初始化 n = (tab = resize()).length; //通过resize()办法获取调配空间。 if ((p = tab[i = (n - 1) & hash]) == null) //如果新的地位是空的，则间接放入，否者要解决抵触 tab[i] = newNode(hash, key, value, null); //将value封装成新的node else { //解决抵触 Node<K,V> e; K k; // 留神p的赋值在 第二个if外面，它示意的是抵触地位所寄存的节点。如果新传入的节点和以后node的hash和key雷同，则上面再解决 if (p.hash == hash && ((k = p.key) == key || (key != null && key.equals(k)))) e = p; else if (p instanceof TreeNode) //基于红黑树的插入 e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value); else { //基于链表的插入 for (int binCount = 0; ; ++binCount) { if ((e = p.next) == null) { p.next = newNode(hash, key, value, null); if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st treeifyBin(tab, hash); break; } if (e.hash == hash && ((k = e.key) == key || (key != null && key.equals(k)))) break; p = e; } } //更新以后传入的值到以后node中。返回之前的oldValue if (e != null) { // existing mapping for key V oldValue = e.value; if (!onlyIfAbsent || oldValue == null) e.value = value; afterNodeAccess(e); return oldValue; } } ++modCount; //批改次数+1， if (++size > threshold) //空间大小，如果超过了阈值，要扩容 resize(); afterNodeInsertion(evict); return null;}其中波及的重点办法：resize()办法，返回新调配的空间。
final Node<K,V>[] resize() { Node<K,V>[] oldTab = table;//获取老的table空间 int oldCap = (oldTab == null) ? 0 : oldTab.length; //获取老的容量 int oldThr = threshold; //获取老的阈值 int newCap, newThr = 0; if (oldCap > 0) { if (oldCap >= MAXIMUM_CAPACITY) { threshold = Integer.MAX_VALUE; return oldTab; } //扩容两倍 else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY && oldCap >= DEFAULT_INITIAL_CAPACITY) newThr = oldThr << 1; // double threshold } else if (oldThr > 0) // initial capacity was placed in threshold，构造函数指定了阈值 newCap = oldThr; else { // 第一次初始化 oldCap=0,oldThr=0 newCap = DEFAULT_INITIAL_CAPACITY; //默认大小，16 newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY); //默认计算方法，16*0.75,12 } if (newThr == 0) { //初始化阈值 float ft = (float)newCap * loadFactor; newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ? (int)ft : Integer.MAX_VALUE); } threshold = newThr; //将新计算出来的值，赋值 @SuppressWarnings({"rawtypes","unchecked"}) Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap]; //重新分配空间。 table = newTab; //扩容后的空间赋值（此时，空间还是空的） if (oldTab != null) { //如果老的空间，不是空的，那么须要元素转移 for (int j = 0; j < oldCap; ++j) { //遍历进行转移 Node<K,V> e; if ((e = oldTab[j]) != null) { //将元数取出来 oldTab[j] = null; if (e.next == null) newTab[e.hash & (newCap - 1)] = e; else if (e instanceof TreeNode) ((TreeNode<K,V>)e).split(this, newTab, j, oldCap); else { // preserve order Node<K,V> loHead = null, loTail = null; Node<K,V> hiHead = null, hiTail = null; Node<K,V> next; 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;}4.Node构造
static class Node<K,V> implements Map.Entry<K,V> { final int hash; //节点的hash值 final K key; //存入的key值 V value; //寄存的值 Node<K,V> next; //下一个节点....}留神hashMap和LinkedList的区别，后者是双向的，而hashMap中的Node是单向的。
5.get()操作
public V get(Object key) { Node<K,V> e; return (e = getNode(hash(key), key)) == null ? null : e.value; //代码内容在这里}调用getNode()办法，计算hash(key)值，通过Hash来取得node
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) { //第一个 检测数组中的hash定位取得第一个Node if (first.hash == hash &&((k = first.key) == key || (key != null && key.equals(k)))) return first; //第一个不是，那么就是后续节点中，可能是链表模式，可能是红黑树 if ((e = first.next) != null) { if (first instanceof TreeNode) //如果是红黑树，通过getTreeNode()办法取得 return ((TreeNode<K,V>)first).getTreeNode(hash, key); //链表模式，间接循环遍历取得。 do { if (e.hash == hash &&((k = e.key) == key || (key != null && key.equals(k)))) return e; } while ((e = e.next) != null); } } return null;}链表模式的获取比较简单，红黑树的取得，咱们放在上面红黑树独自进行介绍。
三，TreeMap
TreeMap和之前的两个map就不同了，它没有应用哈希表，而是间接应用红黑树解决，它的字段只保留了根节点
private final Comparator<? super K> comparator; //排序比拟器private transient Entry<K,V> root; //根节点private transient int size = 0;private transient int modCount = 0;1.get()
public V get(Object key) { Entry<K,V> p = getEntry(key); return (p==null ? null : p.value);}getEntry()
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); //左右分流 if (cmp < 0) p = p.left; else if (cmp > 0) p = p.right; else return p; } return null;}2.put() 波及红黑树的操作，所以代码比拟长
public V put(K key, V value) { Entry<K,V> t = root; if (t == null) { compare(key, key); // type (and possibly null) check 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; 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;}3.remove()
public V remove(Object key) { Entry<K,V> p = getEntry(key); if (p == null) return null; V oldValue = p.value; deleteEntry(p); //理论办法 return oldValue;}总结：
HashMap体现得更像TreeMap和HashTable的结合体。
最初
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