collections

问题 Does ObjectiveC provide a collection for Key-Value-Pairs, that allow a key to occur multiple times? I try to parse a xml file into some simple structure. Every things is already working with nested NSDictionary, but now xml elements can occur multiple times. Edit: My Solution I choose an NSArray with KeyValuePairs, it turned out that I need something that is order sensitive, NSDictionary was not possible. Sideeffect: NSFastEnumeration is easy to implement this way for my collection. 回答1: No,

问题 In Java, 'Set' and 'List' are interfaces derived from 'Collection' interface. If we use the code: import java.util.*; public class SetExample{ public stactic void main(String[] args){ Set set = new HashSet(); //do something ..... } } Is there a class 'Set' in "Collection" API that we are creating an object ('set') of? or we are instantiating a interface 'Set'? Am really confused.......:O 回答1: java.util.Set is an interface, not a class. So Set set = new HashSet(); creates an object that is a

问题 I use the following snippet to filter the list of selected users, where isSelected is a boolean variable. Is there a simpler way (helper function) to populate the selectedUsers collection instead of writing the following lines of code. List<User> selectedUsers = new ArrayList<User>(0); for (User user : this.getUsers()) { if (user.isSelected()) { selectedUsers.add(user.getId()); } } 回答1: You can use the filter function from the Google Collections; however, you will still need to construct a

问题 I want to read lines from a file into a Set or List. Is there a standard utility for doing this? If these lines are of the form [key]=[value] I can do: Properties properties = new Properties(); properties.load(new FileInputStream(file)); The values are single entries, one per line, each value becomes an entry in the Set/List I know it can be done with LineReader, InputStreams and plenty of boilerplate but I'm looking to avoid this. 回答1: yes, the Properties class itself provides accessor

问题 Hello I've this piece of code: public static void main(String[] args) { Set<Integer> set1 = new HashSet<Integer>(); Set<Integer> set2 = new HashSet<Integer>(); set1.add(1); set1.add(2); set1.add(3); set1.add(4); set1.add(5); set2.add(4); set2.add(5); set2.add(6); set2.add(7); set2.add(8); SetView<Integer> x = Sets.intersection(set1, set2); set1.removeAll(x); set2.removeAll(x); } and it throws Exception in thread "main" java.util.ConcurrentModificationException at java.util.HashMap

问题 I have a class of persons and list collection as list contains all the values of person class such as : List ilist has 2 values [0]={firstname,lastname} . [1]={firstname2,lastname2} now when i am iterating into the list i am able to print the list but i want to change the value of some parts of my list e.g in index 1 if i want to change the value of firstname2 to firstname3 i am not able to do it . Can anyone tell me how to print the list and then on that index changing any value of the index

问题 I have a class of persons and list collection as list contains all the values of person class such as : List ilist has 2 values [0]={firstname,lastname} . [1]={firstname2,lastname2} now when i am iterating into the list i am able to print the list but i want to change the value of some parts of my list e.g in index 1 if i want to change the value of firstname2 to firstname3 i am not able to do it . Can anyone tell me how to print the list and then on that index changing any value of the index

问题 What is the shortest way to express "get new List B from List A where condition" via a Java 8 lambda? Say I have List<Integer> a = Arrays.asList(1, 2, 3, 4, 5) and I want a new List, B, where the value is > 3. I've read through the new Collections Streams API, but I'm not convinced I have found the best way to do this, and don't want to taint the question with what is probably my less than perfect solution. 回答1: a.stream().filter(x -> x > 3).collect(Collectors.toList()); 来源： https:/

问题 I have a MyBean annotated @XmlRootElement public class MyBean ... Marshalling/Unmarshalling MyBean w/o problems, e.g. JAXBContext jaxbCtx = JAXBContext.newInstance(MyBean.class); Marshaller m = jaxbCtx.createMarshaller(); m.marshal(myBean, writer); How can I use JAXB to marshall/unmarshall a Collection or List? My attempt results in this error: javax.xml.bind.MarshalException - with linked exception: [com.sun.istack.internal.SAXException2: unable to marshal type "java.util.ArrayList" as an

问题 I'd like to do something using a map value for a given key only if the map contains the given key. Naively I would write: Map<String, String> myMap = ...; if(myMap.containsKey(key)) { String value = myMap.get(key); // Do things with value } The code above looks easy to understand, but from a performance point of view, wouldn't it be better the following code? Map<String, String> myMap = ...; String value = myMap.get(key); if(value != null) { // Do things with value } In the second snippet I