collections

问题 Im trying to read a (mongo)userdatabase with java. On the tutorial page I saw how to read the whole collection. I can do something like that: DBCursor cursor = col.find(); while (cursor.hasNext()) { System.out.println(cursor.next()); } Now if I have a collection with users := name, age, password (...) and whatever. Now I would like to find a name with a password. For example for a login process. Lets say I have two strings: String n and p. If there is a user.equals(n) and a password.equals(p)

问题 This question already has answers here : Closed 6 years ago . Possible Duplicate: Why is there not a ForEach extension method on the IEnumerable interface? First, let me specify I am refering to the List<T> method and not the C# keyword. What would be Microsoft's reasoning for having the Foreach method on the List<T> collection but no other collection/enumerable type, specifically IEnumerable<T> ? I just discovered this method the other day, and found it to be very nice syntax for replacing

问题 I am writing a swagger definition file for an API. The API is a for a GET request /path/to/my/api: get: summary: My Custom API description: | Gets a List of FooBar IDs produces: - application/json tags: - FooBar responses: "200": description: successful operation schema: $ref: "#/definitions/MyCustomType" ... MyCustomType: type: object properties: myCustomObject type: ??? # list of string? 回答1: For a list of strings, you can describe as follows: type: array items: type: string Ref: https:/

问题 Commonly, to find element with property of max value I do like this var itemWithMaxPropValue = collection.OrderByDescending(x => x.Property).First(); But is it good way from performance point of view? Maybe I should do something like this? var maxValOfProperty = collection.Max(x => x.Property); var itemWithMaxPropValue = collection .Where(x => x.Property == maxValueOfProperty).First(); 回答1: Both solutions are not very efficient. First solution involves sorting whole collection. Second

问题 I have a java program which goes like this public class PriorityQueueExample { public static void main(String[] args) { PriorityQueue<Integer> pq = new PriorityQueue<Integer>(); pq.add(10); pq.add(1); pq.add(9); pq.add(2); pq.add(8); pq.add(3); pq.add(7); pq.add(4); pq.add(6); pq.add(5); System.out.println(pq); } } My Question is why does not the priority queue sort them. As per the java specs it implements comparable and maintains the sorting order(natural sorting) My output of the program

问题 What I am asking might be a stupid question so please pardon me for that. So it goes like this : List<Boss> bossList = new ArrayList<Boss>(); Boss b = null; for(Employee e : List<Employee> myList){ b = new Boss(); b.setEmployee(e); bossList.add(b); b = null; } So in above scenario, I am creating lot of Boss objects and then de-referencing them(I know I don't need to write "b = null", but i did it for clarity of my question). In normal scenario, I would have marked them to garbage collection,

问题 What I am asking might be a stupid question so please pardon me for that. So it goes like this : List<Boss> bossList = new ArrayList<Boss>(); Boss b = null; for(Employee e : List<Employee> myList){ b = new Boss(); b.setEmployee(e); bossList.add(b); b = null; } So in above scenario, I am creating lot of Boss objects and then de-referencing them(I know I don't need to write "b = null", but i did it for clarity of my question). In normal scenario, I would have marked them to garbage collection,

问题 At first glance it is needed just convert collection to array and pass it to method but this does not work: val toTypedArray = Arrays.asList("a", "b").toTypedArray() Paths.get("", toTypedArray) // <- compilation error here No workarounds??? 回答1: An Array can be passed as an vararg argument by prepending * to it: Paths.get("", *toTypedArray) It’s called spread operator , as I already described in another question here. An instance of List can be converted to vararg as follows: val listAsArr =

问题 A domain model collection (normally a List or IEnumerable) is delegated to a ViewModel. Thats means my CustomerViewModel has a order collection of type List or IEnumerable. No change in the list is recognized by the bound control. But with ObservableCollection it is. This is a problem in the MVVM design pattern. How do you cope with it? UPDATE : Sample of how I do it: public class SchoolclassViewModel : ViewModelBase { private Schoolclass _schoolclass; private ObservableCollection

问题 Collections.sort(ar, new Comparator<Intervals>() { @Override public int compare(Intervals o1, Intervals o2) { return (Integer.valueOf(o1.getEnd())) .compareTo(Integer.valueOf(o2.getEnd())); } }); Hi all, I have the above code in java. Here, ar is a list and Intervals is a class with 2 integer variables : Start and End. I wanted to know what sorting algorithm is followed when we override the compare method of Comparator interface as above. I know, by default Collections.sort() and Arrays.sort(