hashmap

How to remove duplicate values from a HashMap

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问题 I don't know how can best describe my problem but here it is, I'm trying to remove the same names(values) from HashMap<String, String> map = new HashMap<String, String>(); for example if this map contain names like map.put("Vivaldi","Antonio"); map.put("Belucci", "Monica"); map.put("Gudini", "Harry"); map.put("Verdo", "Dhuzeppe"); map.put("Maracci", "Bruno"); map.put("Carleone", "Vito"); map.put("Bracco", "Luka"); map.put("Stradivari", "Antonio"); I want to remove all entries with the value

Spark: Cannot add RDD elements into a mutable HashMap inside a closure

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问题 I have the following code where rddMap is of org.apache.spark.rdd.RDD[(String, (String, String))] , and myHashMap is scala.collection.mutable.HashMap . I did .saveAsTextFile("temp_out") to force the evaluation of rddMap.map . However, even println(" t " + t) is printing things, later myHashMap still has only one element I manually put in the beginning ("test1", ("10", "20")) . Everything in the rddMap is not put into myHashMap . Snippet code: val myHashMap = new HashMap[String, (String,

HashMap key problems

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问题 I'm profiling some old java code and it appears that my caching of values using a static HashMap and a access method does not work. Caching code (a bit abstracted): static HashMap<Key, Value> cache = new HashMap<Key, Value>(); public static Value getValue(Key key){ System.out.println("cache size="+ cache.size()); if (cache.containsKey(key)) { System.out.println("cache hit"); return cache.get(key); } else { System.out.println("no cache hit"); Value value = calcValue(); cache.put(key, value);

add the value in Arraylist<string,List<String>> in hashmap android

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问题 I have to fetch the lis of data. So i have used the arraylist of string with list.here how can i add the value on map. I have used below code: static final String KEY_TITLE = "Category"; static final String KEY_ARTICLE = "article"; static final String KEY_IMAGE = "image"; final ArrayList<HashMap<String, List<String>>> songsList = new ArrayList<HashMap<String, List<String>>>(); XMLParser parser = new XMLParser(); String xml = parser.getXmlFromUrl(URL); // getting XML from URL Document doc =

阅读更多关于 HashMap

HashMap，开发中最常用的数据结构之一，由数组加链表组成，以key-->value键值对形式存在，HashMap的结构如下： HashMap类中有几个关键变量 /**默认的HashMap容器初始化大小16（1右移4位），必须是2的幂次方**/ DEFAULT_INITIAL_CAPACITY = 1 << 4 /**最大的容器大小（2的30次方）**/ MAXIMUM_CAPACITY = 1 << 30 /**默认的加载因子，当HashMap的容量大小超过初始化容量的75%后，会自动进行扩容操作**/ DEFAULT_LOAD_FACTOR = 0.75f /**阈值，当节点数超过8个会自动转化为红黑树**/ TREEIFY_THRESHOLD = 8 /**阈值，当节点数低于6个时会转化为链表**/ UNTREEIFY_THRESHOLD = 6 /**容器树化的最小表容量大小，如果没有达到该值，容器中有太多节点执行resize操作，MIN_TREEIFY_CAPACITY至少应该是TREEIFY_THRESHOLD的4倍，以防止resizing与树化阈值之间的冲突**/ MIN_TREEIFY_CAPACITY = 64 HashMap中有两个重要的内部类，Node、TreeNode Node 代表HashMap中的普通节点（未转化为红黑树之前，在jdk1

Why HashMap initial capacity is not properly handled by the library?

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问题 To create HashMap/HashSet for N elements, we generally do new HashMap((int)(N/0.75F)+1) which is annoying. Why the library has not taken care of this in the first place and allows initialization like new HashMap(N) (should not rehash till N elements) taking care of this calculation (int)(N/0.75F)+1 ? 回答1: Update Updating to reflect changed question. No, there is no such standard API but it seems there is a method Maps.newHashMapWithExpectedSize(int) in guava: Creates a HashMap instance, with

Remove duplicates items from arraylist and hashmap

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问题 I have an arraylist with the name of who pay something, and another arraylist with the cost of each payment. For example: nameArray = Nicola, Raul, Lorenzo, Raul, Raul, Lorenzo, Nicola priceArray = 24, 12, 22, 18, 5, 8, 1 I need to sum the cost of each person. So the array must become: nameArray = Nicola, Raul, Lorenzo price Array = 25, 35, 30 And then, ordering the array by price, so: nameArray = Raul, Lorenzo, Nicola priceArray = 35, 30, 25 I'm using a Map, but the problem now is that I see

access groovy map by dynamic key

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问题 I want a construct a groovy map with dynamic key as below, and want to get the value by dynamic key. But I am not able to access it, it returns null for the same key. class AmazonPackage { public static String WEIGHT = "WEIGHT" } class PackageTests { @Test void "map should return value by dynamic key" () { def map = [ ("${AmazonPackage.WEIGHT}") : 100, "id": "package001"] assert map['id'] == "package001" //assert map[("${AmazonPackage.WEIGHT}")] == 100 //assert map."${AmazonPackage.WEIGHT}" =

What is the fastest for Map keys: Enum.valueOf(~) vs String.hashCode()?

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问题 I am having difficulty comparing the two. So I am appealing to people with more detailed knowledge than me. I have to link a functional object to a name (String ... of course), and the function call is something like this: serviceInstance.useThis(String name, Object parameter); So far I am considering three options for the "backend" of this API: enum + EnumMap pure enum HashMap 1 and 2 are basically the same but 1 is in case I need to reuse the enum for other uses. My main concern boils down

java beginner : How key gets sorted in hashmaps?

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问题 i am new to java and was learning the concepts of hashmaps. I am confused how the keys are sorted in hashmaps. i understood that its based on string length. but i am confused how data is sorted when the string length is same. import java.util.HashMap; import java.util.Iterator; import java.util.Map; import java.util.Set; public class HashMapExample { public static void main(String args[]) { Map<String,String> map = new HashMap<String,String>(20);//SPECIFYING THE TYPE FOR FINDING HASH CODES. /