hashmap

问题 I am using the following programming idiom. I keep a synchronized HashMap with an association of names to objects. To lookup an object for a name I use the following code: MyObject getObject(String name) { synchronized(map) { MyObject obj = map.get(name); if (obj == null) { obj = new MyObjec(); map.put(name, obj); } } } When I then want to work exclusively on such an object I will use a synchronized on such an object: synchronized(obj) { /* do something exclusively on obj (work type I) */ }

问题 I wonder if there is a general all-around solution for a hash map for coordinates (in 2d or 3d, i.e. a vector of doubles)? An example here demonstrates how to create a custom hash-map for pair<int,int> , but it does not seem to be trivial to come-up with an unique map from pair<double,double> (which could represent a 2d coordinate) to size_t . I know that i can use ordered maps by providing comparator object, but for my application there is no need to order them and hash-maps seems to be

问题 Whenever i try to compile this function it gives an error at line 10 --> ErrorMessage : CandidateCode.java.10: illegal start of type static HashMap hm = new HashMap<>(); 1 error I'm trying to compile it on an website's compiler, but when i use netbeans it works completely fine. import java.util.*; public class CandidateCode { static int rep, total = 0, sum = 0, i = 0, j = 0; static HashMap<Integer, Integer> hm = new HashMap<>(); static ArrayList<Integer> al; public static int

问题 Been working on a project for a while now and I've come across a few different complications and solutions that don't seem to pan out together. final public class place implements Serializable { private static final long serialVersionUID = -8851896330953573877L; String world; Double X; Double Y; Double Z; } HashMap<place, Long> blockmap = new HashMap<place, Long>(); // does not work HashMap<Location, Long> blockmap = new HashMap<Location, Long>(); //works First, my hashmap is a hashmap

问题 In a portion of my code, two LinkedHashMaps are created, like so: Map<Byte, Integer> hash1 = new LinkedHashMap<Byte, Integer>(); Map<Byte, Integer> hash2 = new LinkedHashMap<Byte, Integer>(); After that, a for-loop is ran to add values into their respective HashMap, and then the HashMaps are ran through another loop used for packet creation. Would it be better to call .clear() after the second loop is called, or just let the garbage collector take care of it? 回答1: If you don't call clear(),

问题 I have to fetch the data from xml feed and display on android application. my xml feed is looking like: <root> <Categories> <Category name="Books"> <Articles> <article articleid="4537" title="Android" /> <article articleid="4560" title="Java" /> <article articleid="4585" title="PHP" /> <article articleid="4731" title="MySql" /> </Articles> </Category> <Category name="Names"> <Articles> <article articleid="266" title="Dita" /> <article articleid="268" title="Frieda" /> <article articleid="269"

问题 I have a small doubt with the concept of Rehashing in HashMap . Lets say I have a HashMap with size 8 and within that I have an Object(E1) present at index 7. So when we put multiple elements, forcing the HashMap to increase its internal Array size, which will lead to rehashing. So my question goes, After the rehashing, will my Object(E1) be placed at 7th index or will it get a different bucket. Appreciate useful response and references. 回答1: The bucket your key is placed in is a function of

问题 i building a json object that consists of nameValue pairs defined in a Hashmap the issue i am having is when i invoke: jsonObject.put(hashmap); It adds the nameValue pairs like this: name=value instead of name:value Any thoughts? Thanks 回答1: Iterate through the HashMap and put to the jsonObject: Iterator it = mp.entrySet().iterator(); while (it.hasNext()) { Map.Entry pairs = (Map.Entry)it.next(); jsonObject.put(pairs.getKey(), pairs.getValue() ); } 回答2: Use JSONObject constructor. DON"T

问题 Im having some problems with using a json array to populate an imageview using picasso within a gridview. I think i have most of it down but have however run into a but of a problem my plan is to a) collect the json array b) convert to a hashmap c) add it an array list d) pass arraylist to ImageAdaptor e) set the view and add correct data i am currently stuck on d with the following error Error:(97, 41) error: constructor ImageAdapter in class ImageAdapter cannot be applied to given types;

问题 I have the following code which adds some arrays to a hashmap but then I want access those arrays to do some work on them later. I've gotten this far but can't figure the rest out to make it work.... import java.util.HashMap; import java.util.Iterator; import java.util.Map.Entry; public static void main(String[] args) { String[][] layer1 = { {"to1", "TYPE1", "start"}, {"to2", "TYPE1", "start"} }; String[][] layer2 = { {"to3", "TYPE2" ,"item1"}, {"to3", "TYPE2" ,"item2"} }; HashMap<String