HashMap的使用

淡淡的烟草味﹌ 2021-12-03 20:11 276阅读 0赞

## 参考的文档 ##

阅读[JDK1.8 HashMap源码分析][JDK1.8 HashMap]  
阅读源码

## jdk1.8 HashMap的数据结构 ##

数组+链表+红黑树  
HashMap使用hash()方法来决定元素在数组位置，因为hash算法会出现过个元素的的hash()返回的值是一样的，它用链表存放这些hash值相同的元素，jdk1.6是用数组和链表实现的，在1.8里面当链表的长度（阀值）超过8，就会转为红黑树。

## 一些方法的使用 ##

package com.fang.javalearn.javalearn.collection.map; import java.util.ArrayList; import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Random; import java.util.Map.Entry; import java.util.concurrent.CopyOnWriteArrayList; import lombok.extern.slf4j.Slf4j; @Slf4j public class HashMapTest { public static void main(String[] args) { testHashMap(); } private static void testHashMap() { Random ran = new Random(); HashMap<String, Integer> map = new HashMap<>(); map.put("one", ran.nextInt(100)); map.put("two", ran.nextInt(100)); map.put("three", ran.nextInt(100)); // one iterator /* * Iterator it = map.entrySet().iterator(); while (it.hasNext()) { Entry entry = * (Entry) it.next(); log.info("key:" + entry.getKey() + ",value:" + * entry.getValue()); } */ // two iterator 泛型 Iterator<Map.Entry<String, Integer>> iterator = map.entrySet().iterator(); while (iterator.hasNext()) { Map.Entry<String, Integer> entry = iterator.next(); log.info("key:" + entry.getKey() + ",value:" + entry.getValue()); } // log.info("map size {}", map.size()); // contains key log.info("map contains key " + "one:" + map.containsKey("two")); log.info("map contains key" + "nine:" + map.containsKey("nine")); // contains value log.info("contain value 0:" + map.containsValue(new Integer(0))); // remove map.remove("one"); log.info("map contains key " + "one:" + map.containsKey("two")); // clear（） map.clear(); while (iterator.hasNext()) { Map.Entry<String, Integer> entry = iterator.next(); log.info("key:" + entry.getKey() + ",value:" + entry.getValue()); } log.info("map size {}", map.size()); } }

转载于:https://www.cnblogs.com/JuncaiF/p/11168744.html

[JDK1.8 HashMap]: https://www.cnblogs.com/xiaoxi/p/7233201.html