arraylist

问题 I'm working with firebase in a android application and something strange ocurred, in my example I need two snapshots, 1 to get the users inside a list ( I use this snapshot to fill a arraylist of strings with the key of the user) and the other to compare to the users, the strange behavior is that my arraylist is empty after the first snapshot, I used logcat to check it and that Log inside the firstsnapshot returns me 1 as the size of the arraylist, the second returns me 0, dunno how it gets 0

问题 How can I know the instance of java.util.Arrays$ArrayList . I've tried this code snippet but it does not work at all : if (myList instanceof Arrays) { //Do something here. } I have compared the object classtype with ArrayList and I had the same issue. But while I was inspecting the object, the classType was a : class java.util.Arrays$ArrayList The conditional statement below was the only solution I found: else if (myList.getClass().toString().equals("class java.util.Arrays$ArrayList")) { //do

问题 i have an arraylist that do this : ArrayList<Integer> id = new ArrayList<Integer>(); for (int i = 0; i <= 20; i++) { id.add(getResources().getIdentifier("q"+i, "raw", getPackageName()));} this method before a little change is working good but now have force close! and i get this logcat: FATAL EXCEPTION: main java.lang.RuntimeException: Unable to start activity ComponentInfo{yaAli.package313.hossein110/yaAli.package313.hossein110.know}: java.lang.NullPointerException at android.app

问题 I want to sum values of arraylist in hashmap java . Following is my code: Map hm = new HashMap(); for(int i=0; i<dataArray().length; i++){ Arraylist valueHashMap = new Arraylist(); valueHashMap.add(0, aArray[i]); valueHashMap.add(1, bArray[i]); valueHashMap.add(2, cArray[i]); if (hm.containsKey(dArray[i])){ Arraylist newOne = new Arraylist(); newOne.add(hm.get(dArray[i])); valueHashMap.add(newOne); hm.put(dArray[i], valueHashMap); }else{ hm.put(dArray[i], valueHashMap); } } Iterator iterator

问题 This question is unlikely to help any future visitors; it is only relevant to a small geographic area, a specific moment in time, or an extraordinarily narrow situation that is not generally applicable to the worldwide audience of the internet. For help making this question more broadly applicable, visit the help center. Closed 7 years ago . I'm creating a multithread chat in java. When user u1 sends a message to user u2 but user u2 is not connected, user u1 sends the message to the server

问题 I have a problem with displaying the elements of the ArrayList in Java. While returning the ArrayList when its called from the Views to BMIAnalyzier class which contains the dummy values form now. It shows [] [] When java files are run. Views.java Switch(choice[0]){ case 1: //Option 1 to display the data fo subject of given subject id. ArrayList<Records> arraylist = analyzier.find(choice[1]); System.out.println(ArrayList); Break; Case 2: //Option 2 to display the data fo subject from the

问题 I came across a problem while practising Java. I have a class Book which stores the following information: id (int), author and title and I have another class BookShelf which store a collection of books using a Vector/ArrayList and have the following methods: addBook: takes in a book object as input, adds the object into the bookshelf, method returns nothing. returnListOfBooks: takes in no argument and returns a Vector/ArrayList of all books sorting by title in alphabetical order.

问题 I have following java class package com.picvik.model; import java.util.Date; public class ViewAlbum { private Integer albumid; private String albumname; private String description; private String location; private Date date; private Integer uid; public Integer getAlbumid() { return albumid; } public void setAlbumid(Integer albumid) { this.albumid = albumid; } public String getAlbumname() { return albumname; } public void setAlbumname(String albumname) { this.albumname = albumname; } public

问题 I've run into a problem when detecting collision between the player and many of the same objects(in this case wall tiles). The problem is that my program only detects the collision when I'm in contact with the last added wall tile. This is written in java... I am using rectangles(their intersects method) to detect collision. Code samples: Update tiles: for (int i = 0; i < wallTileArr.size(); i++) { wallTile = wallTileArr.get(i); wallTile.update(p); if(wallTile.getBounds().intersects(Screen

问题 Hello I'm working on a project where I have to insert each object of type "Person" in an ArrayList of type "Person" to a Gridview in eclipse android. My intentions are to display a picture along with the Person's name (similar to Instagram). Here's what I have tried so far but this doesn't seem to work as I want it to and hard to understand. Do yall have any better solutions? ArrayList<Person> dbPersons = dop.getPersons(dop); //This is where I populate my list int[] imageId = { R.drawable