Java基础-HashSet源码分析
package com.hspedu.hashset_; import java.util.HashSet; @SuppressWarnings({"all"}) public class Course521 { public static void main(String[] args) { // HashSet源码1、2 /* * debugger源码分析: * 1、new HashMap(); * 给定默认的加载因子 this.loadFactor = DEFAULT_LOAD_FACTOR; // 0.75 * 2、add方法 => map.put => putVal(key, value) key是需要存放的元素,value是static值 * 其中hash(key)会根据需要保存的集合元素key计算获得一个hash值,集合元素存放的位置i = (n - 1) & hash,再判断i的位置是否为null * 最终返回null则表示添加成功,返回是查询到的对象,表示已经存在该对象,添加失败 * * 添加相同元素的情况: * (1)定义一个临时的节点p指向该位置链表的第一个元素对象,p.hash和添加的元素传入putVal方法的hash比较, * 并且满足key(添加的元素对象)和指向的node节点的key是同一个对象,或者key不为null时,通过equals方法比较内容相同时,不添加对象 * (2)判断p位置是否是红黑树结构,调用putTreeVal比较判断 * (3)不满足1、2则为链表的形式,for循环遍历比较,e = p.next,即直接和第二个元素对象进行比较,p = e使得p指向的位置依次下移比较... * 如果把元素添加到最后null的位置,会判断索引值,如果索引>=7,即满足8个元素对象时,加入第九个元素时创建树结构(创建树时如果数组tab的长度不满足64先扩容数组) * */ HashSet hashSet = new HashSet(); hashSet.add("java"); hashSet.add("php"); hashSet.add("java"); System.out.println("hashSet = " + hashSet); /* final V putVal(int hash, K key, V value, boolean onlyIfAbsent, boolean evict) { Node<K,V>[] tab; Node<K,V> p; int n, i; if ((tab = table) == null || (n = tab.length) == 0) n = (tab = resize()).length; // newCap = DEFAULT_INITIAL_CAPACITY; 初始化给定默认值16 if ((p = tab[i = (n - 1) & hash]) == null) // 判断tab[i]位置上是否已经存在元素 tab[i] = newNode(hash, key, value, null); // 如果为null则新增节点对象 else { // 如果为非null则判断 Node<K,V> e; K k; if (p.hash == hash && ((k = p.key) == key || (key != null && key.equals(k)))) // 比较改节点位置元素的hash key e = p; else if (p instanceof TreeNode) e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value); else { 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; } } if (e != null) { // existing mapping for key V oldValue = e.value; if (!onlyIfAbsent || oldValue == null) e.value = value; afterNodeAccess(e); return oldValue; } } ++modCount; if (++size > threshold) // 判断size是否达到临界的阈值capacity * 0.75,例如初始化16*0.75=12 resize(); afterNodeInsertion(evict); return null; } */ } }
package com.hspedu.hashset_; import java.util.HashSet; @SuppressWarnings({"all"}) public class Course523 { public static void main(String[] args) { // HashSet源码3 /* * 1、HashSet第一次添加元素,底层tab数组扩容到16,临界值是16*0.75=12(0.75是底层的final加载因子) * 2、数组到临界值12时,就会扩容到16*2=32,临界值32*0.75=24以此类推 * 3、如果数组一个位置的链表到达8时,并且tab数组容量到64时,则创建树结构储存 * 4、如果数组一个位置的链表到达8时,但是tab数组容量没有到64,仍然是2倍的数组扩容先扩容数组tab大小 * * (debugger过程可以看出hash计算的值就是hashCode的值) * * */ HashSet hashSet = new HashSet(); // for (int i = 1; i <= 100; i++) { // hashSet.add(i); // } for (int i = 1; i <= 12; i++) { hashSet.add(new A(i)); } /* // 如果数组上一条链表的长度达到8时,会调用treeifyBin树化方法 final void treeifyBin(Node<K,V>[] tab, int hash) { int n, index; Node<K,V> e; if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY) // MIN_TREEIFY_CAPACITY = 64; 数组的如果小于64则优先resize扩容 resize(); else if ((e = tab[index = (n - 1) & hash]) != null) { TreeNode<K,V> hd = null, tl = null; do { 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) hd.treeify(tab); } } final Node<K,V>[] resize() { Node<K,V>[] oldTab = table; int oldCap = (oldTab == null) ? 0 : oldTab.length; int oldThr = threshold; int newCap, newThr = 0; if (oldCap > 0) { if (oldCap >= MAXIMUM_CAPACITY) { threshold = Integer.MAX_VALUE; return oldTab; } else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY && // 数组扩容2倍数,大小从初始16->32 oldCap >= DEFAULT_INITIAL_CAPACITY) newThr = oldThr << 1; // double threshold // 数组临界扩容阈值,大小从初始12->24 } else if (oldThr > 0) // initial capacity was placed in threshold newCap = oldThr; else { // zero initial threshold signifies using defaults newCap = DEFAULT_INITIAL_CAPACITY; // 默认容量16->32 newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY); // 默认阈值12->24 } if (newThr == 0) { float ft = (float)newCap * loadFactor; newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ? (int)ft : Integer.MAX_VALUE); } threshold = newThr; // 更新临界阈值 @SuppressWarnings({"rawtypes","unchecked"}) Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap]; // 更新table数组 table = newTab; if (oldTab != null) { for (int j = 0; j < oldCap; ++j) { Node<K,V> e; if ((e = oldTab[j]) != null) { 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; } */ } } class A { private int n; public A(int n) { this.n = n; } // 重写hash使添加的元素在一条链表上 @Override public int hashCode() { return 100; } }