collections

问题 Consider the following Code : import java.util.*; class Employee { String name; public Employee(String nm) { this.name=nm; } } public class HashMapKeyNullValue { Employee e1; public void display(){ Employee e2=null; Map map=new HashMap(); map.put(e2, "25"); System.out.println("Getting the Value When e2 is set as KEY"); System.out.println("e2 : "+map.get(e2)); System.out.println("e1 : "+map.get(e1)); System.out.println("null : "+map.get(null)); map.put(e1, ""); System.out.println("Getting the

问题 No one said that OrderedDictionary is having two copies of elements, one in a hashtable and other in a list, I can't find complexity measurements at MSDN for OrderedList. thanks 回答1: Have a look at OrderedDictionary: A generic implementation of IOrderedDictionary This implementation of an ordered dictionary is very good at lookup operations: the array allows O(1) lookups by index, and the hashtable allows O(1) lookups by key. However, the necessity of keeping the array synchronized with the

问题 I am looking for sample code which explains Guava ForwardingList class. Basically I am implementing a custom ArrayList class which will be used to solve this requirement mentioned in my earlier SO question. I never used Google collection before. But by just looking at the JavaDoc of ForwardingList, I think I can implement my custom class by sub classing ForwardingList. 回答1: ForwardingList (which extends ForwardingCollection, which in turn extends ForwardingObject) implements the decorator

问题 I come from a Javascript background (where properties can be accessed through both . and [] notation), so please forgive me, but what, exactly, is the difference between the two in Python? From my experimentation it seeems that [] should always be used, both to get the index of a list or set and to get the value from a certain key in a dictionary . Is this correct, and, if not, when do you use a . in Python? 回答1: The dot operator is used for accessing attributes of any object. For example, a

问题 A common senario: A model with a collection of item models. E.g a House with a collection of People. How to structure this correctly for MVVM - particulary with regard to updating the Model and ViewModel collections with additions and deletes? Model House contains a collection of model People (normally a List<People> ). View model HouseVM contains the House object that it wraps and an ObservableCollection of view model PeopleVM ( ObservableCollection<PeopleVM> ). Note that we end up here with

问题 This is driving me crazy. I don't know how to update the app widget from the configuration activity, even with the recommended practises. Why the update method is not called on the app widget creation is beyond my understanding. What I'd like: an app widget containing a collection (with a listview) of items. But the user needs to select something, so I need a configuration activity. The configuration activity is a ListActivity : @TargetApi(Build.VERSION_CODES.HONEYCOMB) public class

问题 In Python, How can one subtract two non-unique, unordered lists? Say we have a = [0,1,2,1,0] and b = [0, 1, 1] I'd like to do something like c = a - b and have c be [2, 0] or [0, 2] order doesn't matter to me. This should throw an exception if a does not contain all elements in b. Note this is different from sets! I'm not interested in finding the difference of the sets of elements in a and b, I'm interested in the difference between the actual collections of elements in a and b. I can do

问题 I don't understand why this code does not work. foreach (DataRow dataRow in dataTable.Rows) { if (true) { dataRow.Delete(); } } 回答1: Even though DataRow.Delete doesn't modify the state of the collection, Microsoft documentation states that you shouldn't call it while iterating over the collection: Neither Delete nor Remove should be called in a foreach loop while iterating through a DataRowCollection object. Delete nor Remove modify the state of the collection. The best solution is usually to

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 5 years ago . I recently heard Vector is a Legacy class , then I read on a website that Legacy classes are used to save Objects before Collections came. So, why these are not called Deprecated classes, why Legacy ? 回答1: Legacy classes and interfaces are the classes and interfaces that

问题 Jon Skeet recently raised an interesting programming topic on his blog: "There's a hole in my abstraction, dear Liza, dear Liza" (emphasis added): I have a set – a HashSet , in fact. I want to remove some items from it… and many of the items may well not exist. In fact, in our test case, none of the items in the "removals" collection will be in the original set. This sounds – and indeed is – extremely easy to code. After all, we’ve got Set<T>.removeAll to help us, right? We specify the size