collections

问题 This question already has answers here : What is a raw type and why shouldn't we use it? (15 answers) Closed 2 years ago . I am learning java right now. While writing code for traversing ArrayList using Iterator I have to use the class name before using the iterator's object with next() function. Can anybody help me with this? import java.util.*; public class arraylistwithuserdefinedclass { public static void main(String[] args) { ArrayList<UserId> details=new ArrayList<UserId>(); UserId a=

问题 This question already has answers here : What is a raw type and why shouldn't we use it? (15 answers) Closed 2 years ago . I am learning java right now. While writing code for traversing ArrayList using Iterator I have to use the class name before using the iterator's object with next() function. Can anybody help me with this? import java.util.*; public class arraylistwithuserdefinedclass { public static void main(String[] args) { ArrayList<UserId> details=new ArrayList<UserId>(); UserId a=

问题 Is there any way I can modify the HashMap values of a particular key while iterating over it? A sample program is given below: public static void main(String[] args) { HashMap<Integer,ArrayList<String>> hm = new HashMap<Integer, ArrayList<String>>(); ArrayList<String> ar = new ArrayList<String>(); for(int i=0;i<50;i++){ ar.add(Integer.toString(i)); } hm.put(1, ar); for(String s:hm.get(1)){ hm.get(1).add("hello"); } } Error Thrown: Exception in thread "main" java.util

问题 Is there any way I can modify the HashMap values of a particular key while iterating over it? A sample program is given below: public static void main(String[] args) { HashMap<Integer,ArrayList<String>> hm = new HashMap<Integer, ArrayList<String>>(); ArrayList<String> ar = new ArrayList<String>(); for(int i=0;i<50;i++){ ar.add(Integer.toString(i)); } hm.put(1, ar); for(String s:hm.get(1)){ hm.get(1).add("hello"); } } Error Thrown: Exception in thread "main" java.util

问题 I'm running into an isssue when I try to create a collection of collections using backbone js. Here is the code : Models and Collections : var Track = Backbone.Model.extend({ defaults : { title : "" } }) var TrackCollection = Backbone.Collection.extend({ model : Track, }) var Playlist = Backbone.Model.extend({ defaults : { name : "", tracks : new TrackCollection, } }) var PlaylistCollection = Backbone.Collection.extend({ model : Playlist, }) Creation of the playlist collection : var playlists

问题 This is a bit of a long question, but I've made it as terse as possible, so please bear with me. It looks to me like a bug in the XmlSerializer class but before I file it with Microsoft I'd like to see if there's anything I've missed, which is entirely possible. I'm attempting to generate the following XML as a representative case, which is essentially a collection of collections, but where the outer collection has additional elements: <Links> <Name /> <Group> <Link /> <Link /> </Group>

问题 Below is the method add() of Java List Interface ; if I loop through it 7 times adding i to the 0 th position like so. for (int i = 0; i < 7; i++) { list.add(0, i); } Wouldn't it overwrite the value at that position, so I would end up with just one value of 6 in the list? Am I right, in assuming that? 回答1: No, if you add at a position, it shifts everything starting at that position to the right. So if you actually did this, you should end up with the following list: [6, 5, 4, 3, 2, 1, 0] Read

问题 Below is the method add() of Java List Interface ; if I loop through it 7 times adding i to the 0 th position like so. for (int i = 0; i < 7; i++) { list.add(0, i); } Wouldn't it overwrite the value at that position, so I would end up with just one value of 6 in the list? Am I right, in assuming that? 回答1: No, if you add at a position, it shifts everything starting at that position to the right. So if you actually did this, you should end up with the following list: [6, 5, 4, 3, 2, 1, 0] Read

问题 so I have a Mission entity connected to an Option entity through a ManyToMany relationship. At the time of creating a new mission it is possible to add several options (this point is ok). Now when updating a mission, when I add a new option it overwrites the last option if it already exists otherwise it fits well. I want to be able to add as many options when modifying a mission without overwriting the last existing option. I post my code: Mission entity : /** * @var ArrayCollection $options

问题 I have below HashMap(to.String()) printed below. HashMap<String, HashMap<String, HashMap<String, Integer>>> abc = new HashMap<>(); HashMap abc = {disabled={account={testConfiguration=1, iterate=1}}} I want to append {group={iterate=1}} to existing map if key disabled matches. Finally my map should look like below, how can I achieve it? HashMap abc = {disabled={account={testConfiguration=1, iterate=1}, {group={iterate=1}}} 回答1: I think you want this: abc.computeIfPresent("disabled", (k,v) -> {