20.HashMap添加，查找，删除，迭代练习

package com.example.test4;import java.util.ArrayList;import java.util.Iterator;/** *  * HashMap添加，查找，删除，迭代练习 *  * 存在问题： *  * 1.entryList()函数中，将表中元素转为添加到list集合变量i应该<table.length(桶的总个数) *   而不是size(已使用桶的个数) *    * 2.在扩容函数中，计算当前节点在新的HashMap中桶对应的Id应该是： *   int newBucketId = node.getKey().hashCode() % newCapacity; *   而不是： *   int newBucketId = node.hashCode() % newCapacity; */interface Map<K, V>{interface Entry<K, V>{K getKey();V getValue();}V put(K key, V value);V get(K key);ArrayList<Map.Entry<K, V>> entryList();int getBucket();void remove(K key);}class HashMap<K, V> implements Map<K, V>{static class Entry<K, V> implements Map.Entry<K, V>{K key;V value;Entry<K, V> next;public Entry(K key, V value){this.key = key;this.value = value;this.next = null;}@Overridepublic K getKey() {// TODO Auto-generated method stubreturn this.key;}@Overridepublic V getValue() {// TODO Auto-generated method stubreturn this.value;}}Entry<K, V>[] table;int size;/** *  * @param initCapacity   *  * HashMap的初始容量，表示桶的个数 *  * size表示已使用桶的个数 */public HashMap(int initCapacity){if (initCapacity < 0){throw new IllegalArgumentException("Illegal initial capacity: " + initCapacity);}table = new Entry[initCapacity];size = 0;}/** *  * 向HashMap中添加元素 *  * 1.key的哈希码对桶的长度求模，得到桶的Id *  * 2.若该位置桶的引用为空，直接将元素添到该位置，并通过桶的总个数以及已经使用桶的个数 *   之比是否大于0.75来判断该HashMap是否需要扩容 *    * 3.引用不为空时，判断是否key相同的元素，若存在，直接替换value至当前value，并返回oldValue *   不存在，使用头插法将新元素以链表的形式插入该桶的后面 */@Overridepublic V put(K key, V value) {// TODO Auto-generated method stubint bucketId = key.hashCode() % table.length;if (table[bucketId] == null){table[bucketId] = new Entry<K, V>(key, value);size++;if (((double)size)/table.length > 0.75){resize(2 * table.length);}}else{Entry<K, V> node = table[bucketId];for (; node != null; node = node.next){if (node.getKey().equals(key)){V oldValue = node.getValue();node.value = value;return oldValue;}}node = new Entry<K, V>(key, value);node.next = table[bucketId].next;table[bucketId] = node;}return null;}/** *  * 从HashMap中得到对应key的value *  * 1.使用key的哈希码对桶的长度长度求模，得到对应Id号的桶 * 2.该桶为空，直接返回 * 3.若不为空，按照链表的形式从table[bucketId]位置开始遍历 */@Overridepublic V get(K key) {// TODO Auto-generated method stubint bucketId = key.hashCode() % table.length;if (table[bucketId] == null){return null;}Entry<K, V> node = table[bucketId];for (; node != null; node = node.next){if (node.getKey().equals(key)){return node.getValue();}}return null;}/** * 将HashMap中的元素添加到List集合当中便于迭代，遍历 */@Overridepublic ArrayList<com.example.test4.Map.Entry<K, V>> entryList() {// TODO Auto-generated method stubArrayList<com.example.test4.Map.Entry<K, V>> list = new ArrayList<com.example.test4.Map.Entry<K, V>>();for (int i = 0; i < table.length; i++){Entry<K, V> node = table[i];for (; node != null; node = node.next){list.add(node);}}return list;}@Overridepublic int getBucket() {// TODO Auto-generated method stubreturn table.length;}/** * 从HashMap中删除关键字为key的元素 */@Overridepublic void remove(K key) {// TODO Auto-generated method stubint bucketId = key.hashCode() % table.length;if (table[bucketId] == null){return;}if (table[bucketId].getKey().equals(key)){table[bucketId] = table[bucketId].next;return;}Entry<K, V> prev = table[bucketId];Entry<K, V> cur = table[bucketId].next;for (; cur != null; cur = cur.next){if (cur.key.equals(key)){prev.next = cur.next;return;}prev = cur;}}/** *  * @param newCapacity  对HashMap扩容时桶的新的个数 *  * 对每一个id对应链表进行遍历是因为之前元素对应桶的Id在新表中桶的Id会有所改变 */public void resize(int newCapacity){//应用扩容前的Entry数组Entry<K, V>[] oldTable = table;//初始化一个容量为之前2倍的Entry数组Entry<K, V>[] newTable = new Entry[newCapacity];for (int i = 0; i < oldTable.length; i++){Entry<K, V> node = oldTable[i];if (node != null){//释放之前Entry数组的引用oldTable[i] = null;do{Entry<K, V> nextNode = node.next;//得到该元素在扩容之后的HashMap中桶的Id值int newBucketId = node.getKey().hashCode() % newCapacity;//使用头插法将该元素插入到桶Id为newBucketId位置的链表上if (newTable[newBucketId] == null){newTable[newBucketId] = node;}else{node.next = newTable[newBucketId].next;newTable[newBucketId].next = node;}node = nextNode;}while(node != null);}}table = newTable;}}public class TestDemo {public static void main(String[] args) {// TODO Auto-generated method stubMap<Integer, String> map = new HashMap<Integer, String>(10);System.out.println("桶的数量：" + map.getBucket());map.put(1, "aaa");map.put(2, "bbb");map.put(3, "ccc");map.put(4, "ddd");map.put(5, "eee");map.put(6, "fff");map.put(7, "ggg");map.put(8, "hhh");map.put(9, "iii");map.put(10, "jjj");map.put(11, "kkk");Iterator<Map.Entry<Integer, String>> it = map.entryList().iterator();while (it.hasNext()){Map.Entry<Integer, String> entry = it.next();System.out.println(entry.getKey() + ":" + entry.getValue());}System.out.println("桶的数量：" + map.getBucket());}}