linkedhashmap | 易学教程

Is there a way to implement an array of LinkedHashMap?

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问题 I am trying to implement an array of LinkedHashMap but I don't know if it's possible... For the moment my code looks like as follows : public class LHMap { public static void main(String[] args) { LinkedHashMap<String, Integer>[] map = null; for (int i = 0; i < 5; i++) { map[i] = new LinkedHashMap<String, Integer>(); } map[0].put("a", 0); System.out.println(map[0].get("a")); } } System.out.println(extracted(map)[0].get("a")); returns a "NullPointerException"... Have you got any idea how to

Sorting LinkedHashMap by value

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问题 How can you sort a LinkedHashMap using the value ? Is there a way to insert entries into a LinkedHashMap so that they are inserted in order based on their value ? 回答1: How can you sort a LinkedHashMap using the value? LinkedHashMap is not sorted , it is ordered by order of insertion. If your goal is to reorder the Map, you might do something like static <K, V> void orderByValue( LinkedHashMap<K, V> m, final Comparator<? super V> c) { List<Map.Entry<K, V>> entries = new ArrayList<>(m.entrySet(

Sorting LinkedHashMap by value

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returning LinkedHashMap from IntStream, Java 8

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问题 I have this code. private static Map<Long, List<TimePitchValue>> alternativeMethod(AudioFormat audioformat, List<ChunkDTO> listChunkDTO, long index, int sizeChunk) { int numBytesPerSample = audioformat.getSampleSizeInBits() / 8; int quantitySamples = sizeChunk / numBytesPerSample; long baseTime = quantitySamples * index; Map<Long, List<TimePitchValue>> mapListTimePitchValue = new LinkedHashMap<>(); for (int i = 0; i < quantitySamples; i++) { int time = i; List<TimePitchValue>

returning LinkedHashMap from IntStream, Java 8

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equivalent LinkedHashmap in C++?

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问题 I have a Java program that I want to convert it to C++. So, there is a Linkedhashmap data structure used in the Java code and I want to convert it to C++. Is there an equivalent datatype for LinkedHashmap in C++? I tried to use std::unordered_map , however, it does not maintain the order of the insertion. 回答1: C++ does not offer a collection template with the behavior that would mimic Java's LinkedHashMap<K,V> , so you would need to maintain the order separately from the mapping. This can be

Java集合：Map接口总结

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一、HashMap 基于哈希表的 Map 接口的实现，允许存入 null 值和 null 键，无序存储且线程不同步； HashMap 初始容量默认为16，扩容一定是2的指数，加载因子默认值为0.75； HashMap采用Iterator方式迭代，可直接迭代键值对；迭代 collection 视图所需的时间与 HashMap 实例的“容量”（桶的数量）及其大小（键-值映射关系数）成比例。所以，如果迭代性能很重要，则不要将初始容量设置得太高（或将加载因子设置得太低）。建议多看源码，如果觉得晦涩可以戳这里看源码解析。安利网址：http://www.admin10000.com/document/3322.html，个人觉得分析的挺好 JDK1.8+HashMap的改进 JDK1.8以前是采用的数组+链表形式存储，JDK1.8+是采用的是数组+链表/红黑树 JDK1.8+，当bucket节点数小于等于6时，转换为链表形式；当节点数大于等于8时，转换为红黑树形式 JDK1.8以前，HashMap的put()方法、get()源码如下： put(): public V put(K key, V value) { // HashMap允许存放null键和null值。 // 当key为null时，调用putForNullKey方法，将value放置在数组第一个位置。 if (key ==

LRU缓存算法-基于LinkedHashMap实现

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近期再做一个项目，是个网站管理系统，涉及多张记录表和栏目表，简单实现网站首页访问后发现速度很忧伤。仔细一想，每次访问，要查询各种表，访问数据库次数太多了，而且很多表里的数据其实在实际中不常改变，所以想到读取后存储在内存中，下次直接返回。于是问题来了，不可能每个网站都存在内存里啊，虽然现在开发阶段没几个网站。这就需要在存新网站数据时清除内存中某些网站的数据，清除谁？我想到了操作系统中的一种页面置换算法——LRU（Least Recently Used）近期最少使用算法。显然HashMap不够用了，我能想到最简单的方法就是用LinkedHashMap，他的一个构造函数： LinkedHashMap<K, V>(int initialCapacity, float loadFactor, boolean accessOrder) Constructs an empty LinkedHashMap instance with the specified initial capacity, load factor and ordering mode. Parameters: initialCapacity the initial capacity loadFactor the load factor accessOrder the ordering mode - true for

Why does specifying Map's initial capacity cause subsequent serializations to give different results?

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问题 I am trying to compare 2 byte[] which are the results of serialization of the same object: 1 byte[] is created by serializing the object the other by deserializing the 1st byte[] and then serializing it again. I do not understand how these 2 arrays can be different. Deserializing the first byte[] should reconstruct the original object, and serializing that object is the same as serializing the original one. So, the 2 byte[] should be the same. However, under certain circumstances they can be

serialize/deserialize a LinkedHashMap (android) java

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问题 So i want to pass a LinkedHashMap to an intent. //SEND THE MAP Intent singlechannel = new Intent(getBaseContext(),singlechannel.class); singlechannel.putExtra("db",shows1);//perase to startActivity(singlechannel); //GET THE MAP LinkedHashMap<String,String> db = new LinkedHashMap<String,String>(); db=(LinkedHashMap<String,String>) getIntent().getSerializableExtra("db"); This one Worked Like a charm with HashMap. But with LinkedHashMap i got a problem i got a runtime error here db=