collections

问题 I'm looking for a way to return an immutable collection from a domain object in Doctrine 2. Let's start with this example from the doc: class User { // ... public function getGroups() { return $this->groups; } } // ... $user = new User(); $user->getGroups()->add($group); From a DDD point of view, if User is the aggregate root, then we'd prefer: $user = new User(); $user->addGroup($group); But still, if we do need the getGroups() method as well, then we ideally don't want to return the

问题 I'm looking for a way to return an immutable collection from a domain object in Doctrine 2. Let's start with this example from the doc: class User { // ... public function getGroups() { return $this->groups; } } // ... $user = new User(); $user->getGroups()->add($group); From a DDD point of view, if User is the aggregate root, then we'd prefer: $user = new User(); $user->addGroup($group); But still, if we do need the getGroups() method as well, then we ideally don't want to return the

问题 System.Collections.Queue class has Queue.Synchronized method which returns a thread-safe Queue implementation. But the generic one, System.Collections.Generic.Queue does not have a Synchronized method. At this point I have two questions in mind: Why doesn't generic one have this method? Is it a framework API design decision? How is the queue returned from Queue.Synchronized is different than ConcurrentQueue<T> class? Thanks. 回答1: The Synchronized() method returns a wrapper queue that slaps a

问题 In Java, i have an arrayList of ip address. how do i find the min and max ? I have used the Collection.min() but it doesnt work given a case like : 192.168.0.1 <--min 192.168.0.250 192.168.0.9 <--max how do i return 192.168.0.1 <--min 192.168.0.250 <--max instead? ArrayList is retrieve from the database. I would need to do this operation per tick (each tick is at 5 sec interval). The number of IP address would hit a max of probably 300. 回答1: Convert the IP address into a long integer, then

问题 I am trying to sort a map based on word frequency (i.e., based on value). For that I have overridden comparator and passed to TreeMap , but I am getting this weird output. public class WordFrequency { public static String sentence = "one three two two three three four four four"; public static Map<String, Integer> map; public static void main(String[] args) { map = new HashMap<>(); String[] words = sentence.split("\\s"); for (String word : words) { Integer count = map.get(word); if (count ==

问题 As we know the List in Kotlin is immutable i.e. you can't do add and remove as below. class TempClass { var myList: List<Int>? = null fun doSomething() { myList = ArrayList<Int>() myList!!.add(10) myList!!.remove(10) } } But if we cast it to ArrayList as below, the add and remove works. class TempClass { var myList: List<Int>? = null fun doSomething() { myList = ArrayList<Int>() (myList!! as ArrayList).add(10) (myList!! as ArrayList).remove(10) } } I just thought this is odd, as myList is

问题 I executed below code and found the output was false . import java.util.Set; import java.util.HashSet; public class Name { private String first, last; public Name(String first, String last) { this.first = first; this.last = last; } public boolean equals(Object o) { if (!(o instanceof Name)) return false; Name n = (Name) o; return n.first.equals(first) && n.last.equals(last); } public static void main(String[] args) { Set<Name> s = new HashSet<Name>(); s.add(new Name("Donald", "Duck")); System

问题 I am trying to write a unit test for a method which takes an IQueryable collection. How should I instantiate the collection in my unit test before I pass it to the method for test? This is the default code in my test IQueryable<Item> Items = null; // TODO: Initialize to an appropriate value And here is what I tried writing IQueryable<Item> Items = new IQueryable<Item>; // TODO: Initialize to an appropriate value Am I making a school boy error? 回答1: Well, you can use .AsQueryable() on any

问题 I'd like to understand the idiomatic way with which to operate over collections of different sizes in clojure. Is there a way I can tell the function 'map' to pad the rest of a collection with some default value? As an example, suppose I have 3 vectors: (def x [1 2 3 4]) (def y [1 2 3 4 5]) (def z [1 2 3 4 5 6 7]) (map + x y z) ; yields (3 6 9 12) In this case, how can I pad x and y with zeroes and have this yield: (3 6 9 12 10 6 7) 回答1: map doesn't do it itself, but you can use a combination

问题 Probably what I'm asking is quite simple but I don't seem to be getting this one out. I have a list of elements containing a Date field and a Time field. The Date field is a regular DateTime and the Time field is a string. Time is formatted like HH:mm and ranges in 24h. Ordering my list by Date is simple by doing List.OrderBy(e => e.Date), but I don't seem to be able to later order it by Time so that the order of the records is according the date and the time. I tried this out but it's