collections

问题 I can't figure out why JCF (Java Collection Framework) does't have a Bag implementation(to allow duplicates and not maintain order). Bag performance would be much better than current Collection implementations in JCF. I know how to implement Bag in java. I know there is a Bag collection in Apache common. I know i can use any implementation as a bag! but there are so much work in other implementations compare to Bag. Why has the Java Collections framework not provided direct implementations

问题 This question already has answers here : What is the point of overloaded Convenience Factory Methods for Collections in Java 9 (6 answers) Closed 2 years ago . I'm studying the factory methods for Immutable collections. I see the Set.of() method has 10 varargs overloading (same for Map.of() ). I really can't understand why there are so many. In the end the function ImmutableCollections.SetN<>(elements) gets called anyway. In the documentation I found this: While this introduces some clutter

问题 I'm trying to determine the best way to accomplish binding a Collection of a custom class to a TreeView. I currently have two custom classes, one held in a Collection, and one held in a Collection inside the first class: Collection<Device> _devices = new Collection<Device>(); class Device { public ulong DeviceID { get; private set; } private List<Capability> _capabilities = new List<Capability>(); public string FriendlyName{ get; set; } public Capability AddCapability(Capability capability) {

问题 I have a collection that can potentially contain thousands of models. I have a view that displays a table with 50 rows for each page. Now I want to be able to cache my data so that when a user loads page 1 of the table and then clicks page 2, the data for page 1 (rows #01-50) will be cached so that when the user clicks page 1 again, backbone won't have to fetch it again. Also, I want my collection to be able to refresh updated data from the server without performing a RESET, since RESET will

问题 I have a List of MyObjects ... MyObject{ int id,String name}. Now I want to split the the list into sublists that have identical "id" values, can any one suggest an efficient approach for doing this. 回答1: // create the thing to store the sub lists Map<Integer, List<MyObject>> subs = new HashMap<Integer, List<MyObject>>(); // iterate through your objects for(MyObject o : list){ // fetch the list for this object's id List<MyObject> temp = subs.get(o.getId()); if(temp == null){ // if the list is

问题 I have a route with a waitOn hook that returns a Meteor.subscribe . Every time the route is triggered, I see the spinner from my loadingTemplate briefly before seeing the actual data. I would have thought that I only had to wait on the subscription to be downloaded once, namely the first time? If I'm doing it wrong, please suggest a better way. 回答1: Have a look at the last comments on this issue. Chris explains that the subscriptions initiated by your router will be stopped once you navigate

问题 I have an array that I want to permutate randomly. In Java, there is a method Collections.shuffle() that can shuffle the elements of a List randomly. It can be used on an array too: String[] array = new String[]{"a", "b", "c"}; // Shuffle the array; works because the list returned by Arrays.asList() is backed by the array Collections.shuffle(Arrays.asList(array)); I tried using this on a Scala array, but the Scala interpreter responds with a lengthy answer: scala> val a = Array("a", "b", "c")

问题 what is the value of using IDictionary here? 回答1: The value of using an interface is always the same: you don't have to change client code when switching to another backend implementation. Consider that profiling your code later shows that a hash table implementation (used in the Dictionary class) isn't suited for your task and that a binary search tree would perform better. If you've coded to an interface then switching the implementation is straightforward. If, however, you've used a

问题 I have an ArrayList to be filtered, and various Guava Predicate s to filter it with. This list will have only 50-100 elements. I was planning on Iterables.removeIf using each predicate in turn. It is perhaps not maximally efficient but never mind (at least removeIf has some optimization for RandomAccess lists) For debugging, I want to concisely log what each predicate did. e.g. Pred0 removed [a, c, g] Pred1 removed [] Pred2 removed [b, f] There are some obvious hack solutions but what would

问题 I am confused as to how the Trie implementation saves space & stores data in most compact form! If you look at the tree below. When you store a character at any node, you also need to store a reference to that & thus for each character of the string you need to store its reference. Ok we saved some space when a common character arrived but we lost more space in storing a reference to that character node. So isn't there a lot of structural overhead to maintain this tree itself ? Instead if a