I’ve got an existing instance of HashMap simply called sale (it is Map<String, Set<String>>) I use it to log customers and items history. Is there a way to create a new instance of HashMap, that effectively reverses this usage? i.e will show each item purchased as a unique key and the corresponding value as a String set of the customer...
I am parsing a xml file into a complex HashMap looking like this: Map<String, Map<String, EcmObject> EcmObject: public class EcmObject implements Comparable, Serializable { private final EcmObjectType type; private final String name; private final List<EcmField> fields; private final boolean pages; // getter, equ...
Hi, I have been working in Java for the last 6 months and have been using Hash Maps What is the basic idea of a Hash Map ? I am using it as it easy for me to store so much data with direct key references rather than having to iterate through an arraylist ? Where is the power of Hash Map seen ? What is the scientific idea behind this ...
I found the following statement: Map is an object that stores key/volume pairs. Given a key, you can find its value. Keys must be unique, but values may be duplicated. For example I have just one key/value pair (3,4). And now I put a new pair (3,5). It will remove the old pair. Right? But if I put (2,4) instead of (3,4) I wil...
I try to do it in the following way: public String getValue(String service, String parameter) { String inputKey = service + ":" + parameter; Set keys = name2value.keySet(); Iterator itr = keys.iterator(); while (itr.hasNext()) { if (inputKey.equal(itr.next())) { return name2value.get(inputKey); ...
The compiler complains about this code: HashMap<String,int> userName2ind = new HashMap<String,int>(); for (int i=0; i<=players.length; i++) { userName2ind.put(orderedUserNames[i],i+1); } It writes "unexpected type" and point on int. If I replace int by String and i+1 by i+"1", the compilation goes OK. What is wrong...
Hi, Given an xml structure like this <gesmes:Envelope> <gesmes:subject>Reference rates</gesmes:subject> <gesmes:Sender> <gesmes:name>European Central Bank</gesmes:name> </gesmes:Sender> <Cube> <Cube time="2010-03-26"> <Cube currency="USD" rate="1.3353"/> <Cube currency="JPY" rate="124.00"/> <Cube currency="BGN" rate="1.9558"/> <Cube cur...
I've got a HashMap and I need to fetch an item by its integer value. I notice there's a containsValue() function, but it would appear I still have to iterate through the map to find the correct index anyway. My question is; why use containsValue() if I'm required to traverse it afterwards? Also, am I missing the point completely? ;-) ...
I am reading up the code of the HashMap class provided by the java 1.6 API and unable to fully understand the need of the following operation (found in the body of put and get methods) : int hash = hash(key.hashCode()); where the method hash() has the following body: private static int hash(int h) { h ^= (h >>> 20) ^ (h >>>...
Hi, I only know that the difference between hashmap and map is that hashmap is implemented with hash function but map is implemented with tree. Could any body add anything more? Based on this, is there any thing hashmap can do but map cannot? ...
I have a text file that looks like this: grn129 agri- ac-214 ahss hud114 ahss lov1150 ahss lov1160 ahss lov1170 ahss lov1210 ahss What is the best way to parse this file using Java if I want to create a HashMap with the first column as the key and the second column as the valu...
Hi all, I have question, I want to develop a programme about extend the hashmap to add putchildren method.. I wrote main class, but now I want to write putChildrenValue method.. My question is : I need to implement a putChildrenValue method with 3 parameters, String key, String key, ObjectValue. It will store the system as described abov...
Hi, I have to classes, ClassA and ClassB and a "many to many" AssociationClass. I want to use a structure to hold the associations between A and B such as I can know, for each instance of A or B, which are their counterparts. I thought of using a Hashmap, with pair keys: Hasmap<Pair<ClassA, ClassB>, AssociationClass> associations; ...
I am trying to perform broad-phase collision detection with a fixed-grid size approach. Thus, for each entity's position: (x,y,z) (each of type float), I need to find which cell does the entity lie in. I then intend to store all the cells in a hash-table and then iterate through to report (if any) collisions. So, here is what I am doing...
I have often heard people talking about hashing and hash maps and hash tables. I wanted to know what they are and where you can best use them for. ...
So I have a java hashmap like below: hMap.put("1", "One"); hMap.put("2", "Two"); hMap.put("3", "Two"); I would like to remove ALL items where the value is "Two" If I do something like: hmap.values().remove("Two"); Only the first one is deleted, I want to remove them all, how can this be done? ...
Say I have a hashmap, $hash = array('fox' => 'some value', 'fort' => 'some value 2', 'fork' => 'some value again); I am trying to accomplish an autocomplete feature. When the user types 'fo', I would like to retrieve, via ajax, the 3 keys from $hash. When the user types 'for', I would like to only retrieve...
Hi all! I am having problems using the update method of scala.collection.immutable.HashMap.I don't see the reason it returns a Map instead of a HashMap. How do I get a new HashMap with a new key-value pair added? ...
Hello I am using this code to check that array is present in the HashMap. public class Test { public static void main(String[]arg) { HashMap<int[],String> map= new HashMap<int[],String>(); map.put(new int[]{1,2}, "sun"); System.out.println(map.containsKey((new int[]{1,2}))); } } But this prints False. How c...
i have a hashmap where every key has many values(stored in a arraylist). How to display the arraylist i.e the values for a particular key in a hashmap in java?? ...