hashmap

问题 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? ;-) 回答1: A map maps a key to a value. If you have a value and you know the map contains this value, why do you need the key anymore? On the other hand, if you really

问题 HashMap savedStuff = new HashMap(); savedStuff.put("symbol", this.symbol); //this is a string savedStuff.put("index", this.index); //this is an int gives me the warning: HashMap is a raw type. References to generic type HashMap<K,V> should be parameterized 回答1: I'm not sure what you're trying to do, but since the example you provided uses hard-coded strings to index the data, it seems like you know what data you want to group together. If that's the case, then a Map is probably not a good

问题 I have the following HashMap where the key is a String and the value is represented by an ArrayList : HashMap<String, ArrayList<String>> productsMap = AsyncUpload.getFoodMap(); I also have another ArrayList<String> foods implemented in my application. My question is, What would be the best way to find out if my HashMap contains a Specific String from my second ArrayList ? I have tried without success: Iterator<String> keySetIterator = productsMap.keySet().iterator(); Iterator<ArrayList<String

问题 Is it ok to rely on (= m (zipmap (keys m) (vals m))) in Clojure 1.3+? Having this behavior makes for slightly more readable code in some situations, eg (defn replace-keys [smap m] (zipmap (replace smap (keys m)) (vals m))) vs. (defn replace-keys [smap m] (into {} (for [[k v] m] [(smap k k) v])) 回答1: I can confirm (officially) that the answer to this is yes. The docstrings for keys and vals were updated in Clojure 1.6 to mention this (see http://dev.clojure.org/jira/browse/CLJ-1302). 回答2: Yes,

问题 In Java 8, this works: Stream<Class> stream = Stream.of(ArrayList.class); HashMap<Class, List<Class>> map = (HashMap)stream.collect(Collectors.groupingBy(Class::getSuperclass)); But this doesn't: Stream<Class> stream = Stream.of(List.class); HashMap<Class, List<Class>> map = (HashMap)stream.collect(Collectors.groupingBy(Class::getSuperclass)); Maps allows a null key, and List.class.getSuperclass() returns null. But Collectors.groupingBy emits a NPE, at Collectors.java, line 907: K key =

问题 I have a hash map table as below, HashMap<String, String> backUpCurency_values = new HashMap<String, String>(); and i want to store these value for future use.. how can i do that? Edit: i will store to Country names and currencyvalue as key and value pair... 回答1: You should just use a for-each loop and iterate through the map like this: SharedPreferences.Editor editor = getSharedPreferences(PREFS_NAME, 0).edit(); for( Entry<String, String> entry : backUpCurency_values.entrySet() ) editor

问题 I'm using hibernate-entitymanager 3.6.4.Final and h2 database 1.3.155 I'm using the H2Dialect. I'm having trouble filtering records by elements in an @ElementCollection. Here is my entity @Entity public class Item { @Id @GeneratedValue(strategy = GenerationType.AUTO) @MapKeyColumn(name="name", length=50) @Column(name="value", length=100) protected Map<String, String> attributes; /* etc. */ } Here is my query : Item item = em.createQuery("FROM Item i JOIN i.attributes a WHERE KEY(a)=

问题 I have an Object that has a HashMap field. When the Object is passed to C, how can I access the field? The Object 's Class has the following fields: private String hello; private Map<String, String> params = new HashMap<String, String>(); 回答1: The answer to your question really boils down to why you'd want to pass a Map to C rather than iterate your Map in Java and pass the contents to C. But, who am I to question why? You ask how to access the HashMap (in your provided code, Map ) field?

问题 I am trying this for some hour but not finding any best approach to achieve iteration of hashmap in reverse order, this is the hashmap I have. Map<Integer, List<String>> map = new HashMap<Integer, List<String>>(); for(Integer key : map.keySet()) { List<String> value = map.get(key); List<Map<String,?>> security = new LinkedList<Map<String,?>>(); for(int ixy = 0; ixy < value.size()-1; ixy++){ security.add(createItem(value.get(ixy), value.get(ixy+1))); } adapter.addSection(Integer.toString(key),

问题 I have a pretty large Hashmap (~250MB). Creating it takes about 50-55 seconds, so I decided to serialize it and save it to a file. Reading from the file takes about 16-17 seconds now. The only problem is that lookups seems to be slower this way. I always thought that the hashmap is read from the file into the memory, so the performance should be the same compared to the case when I create the hashmap myself, right? Here is the code I am using to read the hashmap into a file: File file = new