I need a collection that can lookup a value based on the key and vice versa. For every value there is one key and for every key there is one value. ... |
how can i map ASCII values to appropriate key codes....?
|
I'm pretty new to Java, so don't kill me :)
FileInputStream files = new FileInputStream(path);
Properties prop = new Properties();
try {
...
|
Welcome.
I have a generic void method swap that takes a Map and 2 keys. The method will swap the values associated with the keys in the Map. I already checked that ... |
Java's WeakHashMap is often cited as being useful for caching. It seems odd though that its weak references are defined in terms of the map's keys, not its values. ... |
Below is a small test I've coded to educate myself on references API. I thought this would never throw OOME but it is throwing it. I am unable to figure out ... |
Is there any way to make a key for searching the values in the collections and not returning null keys and values?
|
|
I have a Map that uses a Set for the key type, like this:
Map<Set<Thing>, Val> map;
When I query map.containsKey(myBunchOfThings), it returns false, and I don't understand why. I can iterate through ... |
I have read somewhere that using the class instances as below is not a good idea as they might cause memory leaks. Can someone tell me if if that is a ... |
I want to find out the key for given value from HashMap, currently I have to go through all keys and check its value in map, is there a faster way?
... |
I want to know whether a particular key is present in a HashMap, so i am using containsKey(key) method. But it is case sensitive ie it does not returns true if ... |
I'd like to create new item that similarly to Util.Map.Entry
i.e. that will already contain the structure key,value
The problem is that I can't use Map.Entry itself because apperently it's a ... |
I need to have a sortedMap with these fields for each key
[srcAddr, dstAddr, srcPort, dstPort, protocol] (this is corresponding to a flow)
then this key contains a list of values each containing ... |
Suppose I have a map in Java which looks like this:
{
39:"39 to 41",
41:"41 to 43",
43:"43 to 45",
45:">=45"
}
If the keys are in sorted order(either using treemap or ... |
I'm looking for a Collection type data structure to implement the following. Say I have a class like this:
class Person() {
String homeTown; // key
...
|
Given a Map, how do I look up all keys associated with a particular value?
For example:
Map<Integer, Integer> map = new HashMap<Integer, Integer>();
map.put(1, 5);
map.put(2, 2);
map.put(3, 5);
Collection<Integer> keys = map.values(5); // should return ...
|
I'm using Java 6.
Suppose I have a class which I would like to save its instances into a map. Later on I would like to retrieve instances using only the "key ... |
Is there a way to swap two keys in a map in Java?
ex. for list there is Collections.swap(ArrayList,1,2);
|
I have Map<String, String> which contains elements like: {“a”=”b”, “b”=”c”, “c”=”d”, “z”=”y”, …}.
I need a method:
List<String> getTransitiveKeys(String startKey);// assuming the map is visible somehow as `map`
When getTransitiveKeys(“a”) is called, it will ... |
I'm trying to put some key values in Map and trying to retrieve them in same sequence as they were inserted. For example below is my code
import java.util.*;
import java.util.Map.Entry;
public class HashMaptoArrayExample ...
|
Is there any way to get a key associated with a known value in a map? Normally you know the key and you want to get the value, but I want ... |
The problem is that ; I am retrieving a key value data object pair from database it is like
(select * from xyz ORDER BY letter DESC)
3 z,
2 y,
1 x
And Im putting ... |
Hello I cannot find any info on what I need to do to make two keys seems equal. That is, i need to provide a custom compare method that will be ... |
In one of my Java 6 projects I have an array of LinkedHashMap instances as input to a method which has to iterate through all keys (i.e. through the ... |
If you are mapping Java shorts to a few immutable objects, and it is often the case that a consecutive sequence of short keys (neighbors) map to the same value, ... |
I think my question is similar to this one: How to implement a Map with multiple keys? but with an important difference. In that question (if my understanding of it ... |
what type of java collection that returns multiple values for the same key?
example, I want to return 301,302,303 for key 300.
|
I'm not sure what are prevailing opinions about using dynamic objects such as Sets as keys in Maps.
I know that typical Map implementations (for example, HashMap) use a hashcode to decide ... |
I am working in Java, and have declared two maps as follow:
private Map<MyCustomClass, Integer> map1, map2;
map1 = new HashMap<MyCustomClass, Integer>();
map2 = new HashMap<MyCustomClass, Integer>();
//adding some key value pair into map1
//adding some ...
|
Is there a way to force the jvm that it should clear all WeakReferences (or all keys of a WeakHashMap) if they aren't referenced by regular references anymore?
Triggering a garbage collection ... |
I tried making registry changes by running WScript that runs reg, but it still gets re-routed to WOW6432Node.
Is there a way I can get either a WScript or CMD script (or ... |
I am trying to learn java and I am stumped by this example- I can't find what the key is
public class OrderedArrayMaxPQ<Key extends Comparable<Key>> {
private Key[] pq; ...
|
I'm looking for a Java Map Class that can contains two or more keys for one value. It almost like MultiKeyMap in apache common collections, but it can use ... |
i am facing a problem which is:
I have map containing string and string. When i print that map i can see that there is a key
"0-8166-3835-7". But when i ... |
I need to associate some data with a key for its lifetime, so I am using a WeakHashMap. However, in addition I need to get a key by its corresponding value. ... |
I'm in need of a map with two "joint" or "combined" integer keys pointing to a value (an object). map[K1,K2] = myObject What I have to do now is combine the ... |
I'm trying to understand how WeakHashMap helps in plugging memory leaks. Mostly one would use a String instance as the key. 1 String key = new String("foo"); 2 BigStuff value = new BigStuff(1212); 3 Map map = new WeakHashMap(); 4 map.put(key, valu e); So having a weak key would mean that sooner or later, the variable key will be weakly reachable ... |
Not in the standard libraries, as far as I know. A quick and hopefully-not-too-dirty solution is:public class NonoverwritingMap extends HashMap { public Object put(Object key, Object value) { if (containsKey(key)) throw new IllegalStateException("key already set: " + key); return super.put(key, value); } } It would probably be nicer to instead make this a decorator that could wrap any Map. A quick ... |
Hi All, I am doing a simple application in which I am using a LinkedHashMap implementation of Map to store and pairs. and i am implementing two kinds of search searchByName() and searchByNumber(); while searching by Name i can easily retrieve the results where as while searching through the number there is no direct way to do that according ... |
Hi, Is there any way to get keys on the basis of values in any Collection. Actually my collection looks like this - Service1 Start Service2 Stop Service3 Start Service4 Start Service5 Stop Now I want to get all keys whose values are 'Stop' in a sorted manner. Please give any idea or if any other way .. Thanks in advance. ... |
You cannot remove from a collection (list/set) or map while you are iterating over it. Instead, you will need to actually use the iterator itself, and loose the advantage of the enhanced for loop: for (Iterator i = myMap.keySet().iterator(); i.hasNext(); ) { String o = i.next(); if (!myMap.get(o)) // use auto unboxing :wink: { i.remove(); System.out.println("key with False-Value "+ o); } ... |
Hi all, I am trying to implement a UserList class which should provide the caller with the following functions (among others): Get a User by userId. Get a User by index in the list. Allow for sorting based on userId or name and move elements up and down in the list(using Comparator or something similar). I am having trouble picking the ... |
I have a requirement where I need to fetch data from database Once I fetch it I also need to insert it into a map(a hashmap) for later retrieval. For a query on only one filter let's say "id" this approach is alright. I can easily fetch data filtered on "id" and then store it into hashmap where key value pair ... |
But be careful that you don't change the results of hashCode by changing some field, or your key cannot be found again with get(). Once you add an object to a hash map its hashCode should never change. If it needs to, remove the object from the map first, then change the object, then add it again. For example: Date date ... |
If you want to associate multiple values with a single key in a map, then you need to put those values in to a List and then associate that list with the key. When you want to add a value to the map, you first check if the key already exists. If it does you retrieve the List and add the ... |
|
Is it acceptable to modify the keys of PriorityQueue elements while they are in the queue? That is, can I do something like this: import java.util.*; public class Queue { public static int[] d; static Comparator cmp = new Comparator() { public int compare(Integer a, Integer b) { if(d[a] <= d[b]) return -1; else return 1; } }; public static void ... |
Hello, I am looking for a collection where I could save 3 keys and data. Key1_1, Key2_1, Key3_1, data1_1, data2_1, data3_1 Key1_2, Key2_2, Key3_2, data1_2, data2_2, data3_2 Key1_3, Key2_3, Key3_3, data1_3, data2_3, data3_3 Key1_4, Key2_4, Key3_4, data1_4, data2_4, data3_4 Which collection would suit for it or maybe have I take apache commons collection? Thank you in advance. Best regards, |
Hi to all! Well I' facing the following problem I have two maps(ConcurrentHashMaps),and i want to delete a key based on a specific value from the first map, and with the same key, I want to delete the equal entry, if there is one, on the other map. I try the following code but I think is wrong. Please help: Set |
Hi, If I want to check if a map has a particular key or not. I could think of following two ways to do so. 1. Map.containsKey(KEY) 2. value = Map.get(KEY) and then check if value == null. I think using Map.containsKey() would be faster. But I am not sure of the reason for that. Anybody could throw some light on ... |
Hi, I have some key value pairs. I want to store the same inside a map. But there is a requirement that I need to insert a new key value pair at a position i.e. may be between the first and the second key value pair. Currently I iterate over this and store into a temporary Map and then store after ... |
|
I have a problem where I have a lookup table of about 1,000,000 key/value pairs, and the ids that I have to find are not always exactly complete. Easier to show in an example: IDs ---------- ABCD EFGH IJKL 1234 Lookup Table ---------------- Key/ Value -----/ ------------ ABCD:ILK/ Val1 EI:1234 / Val2 cIJKL:39D9/ Val3 One thing I tried was to nix ... |
Personally, I'd just write a class encapsulating the values, and have a collection of those. List or Set as appropriate, or Map if you wanted to be able to lookup on a unique attribute. Edit: having thought about the original question a bit more, if I was going to use that approach I'd probably use something like "nameToAgeToEmailMap". |
I would like to know if there is a way, for instance in a Hastable or maybe some other data structure, to have more than one key that all map to the same value in the table. For instance, I have a Hashtable of keys containing strings of URL values, each one mapping to an object which contains specific methods and ... |
Hi all, I am reading "Objects first with Java"(third edition) and I am kind of stack on page 145. I am given a little project called techsupport system which simply gets the user input from the terminal window, splits it at the spaces adds the words to a HashSet and passes it to another class which iterates trough the collection. During ... |
|
Hi all I have some key values lited in a property file, and i will get the pairs from the database. So can any one suggest how to go with? Becaz i feel its not of reading the same value every time deom the property file? Also whats the best wat keeping these things in the proprty file as of now ... |
Hello Everyone Let's say I have a System. to access this system, one needs a username and a password. Now i have a Hashtable that maps passwords to their usernames. Now what if i want to store the Firstname and lastname of the person, in case he/she forgets the password or username? Is there a way to associate a key (Password) ... |
|
|
|
|
java.util.Map.keySet will give you a java.util.Set holding the keys of the Map. With that, you can create a java.util.List, passing it the set in the constructor. Then you can sort the list. Then with the sorted list you can get the values. Alternatively, you could use Map.entrySet() to get a set of the key/value pairs (instances of Map.Entry) in the map, ... |
Hi all Ideally I would like a Collection implemenentation that allows two values for each key rather than just a key/value pair. Does anyone know how I can do this? For example if the key was someone's passport number, value 1 would be their name and value 2 would be their age. If not I guess I will have to represent ... |
return; } for (WatchEvent event: key.pollEvents()) { WatchEvent.Kind kind = event.kind(); //This key is registered only for ENTRY_CREATE events, //but an OVERFLOW event can occur regardless if events are //lost or discarded. if (kind == StandardWatchEventKind.OVERFLOW) { continue; } if( kind == StandardWatchEventKind.ENTRY_CREATE) { WatchEvent ev = (WatchEvent)event; Path filename = ev.context(); Path child = dir.resolve(filename); System.out.println(); } else if(kind == ... |