hashmap

问题 Im using ORMLite in my Android app. I need to persist this class, which has a HashMap. What is a good way of persisting it? Its my first time trying to persist a HashMap, also first time with ORMLite so any advice would be greatly appreciated! * Edit * If that makes any difference, the Exercise class is simply a String (that also works as id in the database), and the Set class has an int id (which is also id in database), int weight and int reps. @DatabaseTable public class Workout {

问题 I'm looking for a way to freeze native ES6 Maps. Object.freeze and Object.seal don't seem to work: let myMap = new Map([["key1", "value1"]]); // Map { 'key1' => 'value1' } Object.freeze(myMap); Object.seal(myMap); myMap.set("key2", "value2"); // Map { 'key1' => 'value1', 'key2' => 'value2' } Is this intended behavior since freeze freezes properties of objects and maps are no objects or might this be a bug / not implemented yet? And yes I know, I should probably use Immutable.js, but is there

问题 I have Two Maps Map<String, String> filterMap Map<String, Object> filterMapObj What I need is I would like to convert that Map<String, String> to Map<String, Object> . Here I am using the code if (filterMap != null) { for (Entry<String, String> entry : filterMap.entrySet()) { String key = entry.getKey(); String value = entry.getValue(); Object objectVal = (Object)value; filterMapObj.put(key, objectVal); } } It works fine, Is there any other ways by which I can do this without iterating

问题 I would like to see a simple example of how to override stdext::hash_compare properly, in order to define a new hash function and comparison operator for my own user-defined type. I'm using Visual C++ (2008). 回答1: This is how you can do it class MyClass_Hasher { const size_t bucket_size = 10; // mean bucket size that the container should try not to exceed const size_t min_buckets = (1 << 10); // minimum number of buckets, power of 2, >0 MyClass_Hasher() { // should be default-constructible }

问题 ı am trying to merge more than one hashmaps also sum the values of same key, ı want to explain my problem with toy example as follows HashMap<String, Integer> m = new HashMap<>(); HashMap<String, Integer> m2 = new HashMap<>(); m.put("apple", 2); m.put("pear", 3); m2.put("apple", 9); m2.put("banana", 6); ı tried putall m.putAll(m2); output is as follows {banana=6, apple=9, pear=3} but its result is not true for this problem. ı want to output as {banana=6, apple=11, pear=3} how can ı get this

问题 How can I have a HashMap with unique keys in Java? Or even does this make any sense to have unique keys in HashMap or the keys are unique by default? I am a newbie. thx 回答1: The keys are unique in all maps. The difference between the various maps implementations concern the possibility of null keys, the order of iteration and concurrency issues. 回答2: Hash map key is unique. Add duplicate key, then it will be overwritten. HashMap hm = new HashMap(); hm.put("1", new Integer(1)); hm.put("2", new

问题 What is the most straightforward way to create a hash table (or associative array...) in Java? My google-fu has turned up a couple examples, but is there a standard way to do this? And is there a way to populate the table with a list of key->value pairs without individually calling an add method on the object for each pair? 回答1: Map map = new HashMap(); Hashtable ht = new Hashtable(); Both classes can be found from the java.util package. The difference between the 2 is explained in the

问题 I'm using a HashMap: byte[] key and String value. But I realize that even I put the same object (same byte array and same string value) by using myList.put(TheSameByteArray, TheSameStringValue) into HashMap, the table still inserts a new object with different HashMapEntry. Then function containsKey() cannot work. Can someone explains this for me? How can I fix this? Thanks. (Android Java) @Override public boolean containsKey(Object key) { if (key == null) { return entryForNullKey != null; }

问题 I'm looking for a monad-free, constant access query O(1) associative array. Consider the hypothetical type: data HT k v = ??? I want to construct an immutable structure once: fromList :: Foldable t, Hashable k => t (k,v) -> HT k v I want to subsequently query it repeatedly with constant time access:: lookup :: Hashable k => HT k v -> k -> Maybe v There appears to be two candidate libraries which fall short: unordered-containers hashtables unordered-containers unordered-containers contains

问题 I have a JSON string that resembles the following: { "foo" : "bar", "id" : 1, "children":[ { "some" : "string", "id" : 2, children : [] }, { "some" : "string", "id" : 2, children : [] } ] } I do a JSON parse of this string, and that turns all objects into HashMaps and all arrays into HashMap[]s. My problem is I need a single recursive function to iterate through all nodes of this JSON structure in Java. How can I do this? I was thinking something like: public HashMap findNode(boolean isArray,