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  • How to use ArrayList to store some data using ICollection

    - by Shantanu Gupta
    I want to store few strings into an array using ArrayList. How can I store all the strings at once without using Add function every time. Is it somewhat related to interface ICollection in anyway. Can I use ICollection to store my array. If yes How. ArrayList _1019=new ArrayList("TEN","ELEVEN","TWELVE","THIRTEEN","FOURTEEN","FIFTEEN","SIXTEEN","SEVENTEEN","EIGHTEEN","NINETEEN"); I want to store this in the constructor of a class in C#

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  • Initialization of an ArrayList in one line.

    - by Macarse
    I am willing to create a list of options to test something. I was doing: ArrayList<String> places = new ArrayList<String>(); places.add("Buenos Aires"); places.add("Córdoba"); places.add("La Plata"); I refactor the code doing: ArrayList<String> places = new ArrayList<String>(Arrays.asList("Buenos Aires", "Córdoba", "La Plata")); Is there a better way of doing this? Thanks for reading!

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  • read ArrayList elements

    - by Jessy
    Why it print the wrong output? ArrayList<String> loc = new ArrayList<String>(); This arraylist stored the value of: [topLeft, topLeft, topLeft, bottomLeft, topLeft, bottomLeft, topLeft, topLeft, Left, topLeft] the firs index 0 is = topLeft if(loc.get(1)=="topLeft") System.out.println("same") else { System.out.println("not same") } This program print the wrong output not same instead of same

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  • Java Polynomial Multiplication with ArrayList

    - by user1506919
    I am having a problem with one of my methods in my program. The method is designed to take 2 arraylists and the perform multiplication between the two like a polynomial. For example, if I was to say list1={3,2,1} and list2={5,6,7}; I am trying to get a return value of 15,28,38,20,7. However, all I can get is an error message that says: Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0. I have provided the method below: private static ArrayList<Integer> multiply(ArrayList<Integer> list1,ArrayList<Integer> list2) { ArrayList<Integer> array =new ArrayList<Integer>(list1.size()+list2.size()); for (int i=0;i<array.size();i++) array.add(i, 0); for (int i = 0; i < list1.size(); i++) for (int j = 0; j < list2.size(); j++) array.set(i+j, ((list1.get(i) * list2.get(j))+array.get(i+j))); return array; } Any help with solving this problem is greatly appreciated.

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  • Add objects to Arraylist inside loop and get a list of them outside loops

    - by AgusDG
    Im already done with a method to do a shot on a board (bidimensional array). THe shot goes from the bottom to the top, and depending of the direction, it do bounces on the walls to get to the top. The thing is that I did the method to represent the trayectory with an 'x'. Now, I want to add the coordinates x and y of each position of the shot (b [x][y]) to and Arraylist of Objects Position. public Position(int row,int col) { this.row = row; this.col = col; } The thing is that the method uses a for loop and inside if loops, and I'll need to create the objects inside, and get them outside. I did that : public static ArrayList<Position> showTrayectory (char [][] b , int shotDirection, char bubble){ int row = 0, col = 0; ArrayList<Position> aListPos = new ArrayList<Position>(); Position positionsOfShot = new Position(row,col); START = ((RIGHT_WALL)/2) + shotDirection; boolean shotRight = false; if(shotDirection < 0) shotRight = false; else if(shotDirection > 0) shotRight = true; for(int y = BOTTOM,x = START ;y >= 0;y--) { if(!isOut(y,x) && !emptyCell(y,x)) break; if(x <= LEFT_WALL) shotRight = true; if(x >= RIGHT_WALL) shotRight = false; if(!isOut(y,x) && shotRight == true) { positionsOfShot = new Position(y,x); aListPos.add(positionsOfShot); b[y][x] = SHOT; ++x; } if(!isOut(y,x) && shotRight == false){ positionsOfShot = new Position(y,x); aListPos.add(positionsOfShot); b[y][x] = SHOT; --x; } } // The nested for loops below are for showing the positions // But I dont need it that way // I must get the trayectory from an ArrayList and print it from there for(int y=0;y < b.length;y++){ System.out.println(); for(int x=0;x < b[y].length;x++){ System.out.print(" "+b [y][x]+" "); } } System.out.println("\nTrayectory of the shot ["+shotDirection+"]"); System.out.println("Next bubble ["+bubble+"]"); for( Position ii : aListPos){ System.out.println("(" + positionsOfShot.getFila() + "," + positionsOfShot.getColumna()+")"); } return aListPos; } The sentence " b[y][x] = SHOT; " is still there, to see the proper trayectory of the shot (its not needed that way), but what I need, is getting the trayectory in an ArrayList, and print the trayectory from there. All that I get is a wrong position, and repeated during the number of positions the shot goes through. I need some help. I suppose the problem is that Im creating and adding Position Objects inside an ArrayList inside loops, but in a wrong way. I will need you to explain me how to do it properly ; ) Thanks in advance. I'll add the output for you see better what is that above haha *************************** y b y b g r b g o y g a a r y o y y r b y g r r o b o y y g b a r y r o a y y o o r r g r - - - x - - - - - - - - - x - - - - - - - - - x - - - - - - - - - x - - - - - - - - - x - - - - - - - - - x - - - - - - - x - - - - - - - x - - - - - - - x - - - Trayectory of the shot [1] Next bubble [y] (5,3) (5,3) (5,3) (5,3) (5,3) (5,3) (5,3) (5,3) (5,3) Action?

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  • Returning the index number of an Arraylist in Java

    - by Daniel
    I would like my method public void showClassRoomDetails(String teacherName) to return the Arraylist index number using the teacherName. Thanks import java.util.ArrayList; public class School { private ArrayList<Classroom> classrooms; private String classRoomName; private String teacherName; public School() { classrooms = new ArrayList<Classroom>(); } public void addClassRoom(Classroom newClassRoom, String theClassRoomName) { classrooms.add(newClassRoom); classRoomName = theClassRoomName; } public void addTeacherToClassRoom(int classroomId, String TeacherName) { if (classroomId < classrooms.size() ) { classrooms.get(classroomId).setTeacherName(TeacherName); } } public void showClassRoomDetails(String teacherName) { for (Classroom classroom : this.classrooms) { if (classroom.returnTeacherName().equals(teacherName)) { System.out.println(classroom.returnClassRoomName()); System.out.println(classroom.returnTeacherName()); break; } } } }

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  • Java ArrayList remove dupes without sets

    - by Kieran
    I'm having problems removing duplicates from an ArrayList. It's for an assignment for college. Here's the code I have already: public int numberOfDiffWords() { ArrayList<String> list = new ArrayList<>(); for(int i=0; i<words.size()-1; i++) { for(int j=i+1; j<words.size(); j++) { if(words.get(i).equals(words.get(j))) { // do nothing } else { list.add(words.get(i)); } } } return list.size(); } The problem is in the numberOfDiffWords() method. The populate list method is working correctly, as my instructor has given me a sample string (containing 4465 words) to analyse - printing words.size() gives the correct result. I want to return the size of the new ArrayList with all duplicates removed. words is an ArrayList class attribute. UPDATE: I should have mentioned I'm only allowed to use dynamic indexed-based storage for this part of the assignment, which means no hash-based storage.

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  • How do I pass an ArrayList to method that takes a collection as an input

    - by Ankur
    I want to pass some ArrayList X into method a(Collection someCol) that takes Collection as an input. How can I do this? I thought an ArrayList was a Collection and thus I should be able to "just do it" but it seems that Collection is an interface and ArrayList implements this interface. Is there something I can do to make this work ... if you understand the theory that would also help me and possibly lots of other people. Thanks

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  • Convert an ArrayList to an object array

    - by marionmaiden
    Hello, Is there a command in java for conversion of an ArrayList into a object array. I know how to do this copying each object from the arrayList into the object array, but I was wondering if would it be done automatically. I want something like this: ArrayList<TypeA> a; // Let's imagine "a" was filled with TypeA objects TypeA[] array = MagicalCommand(a);

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  • C# Saving an arraylist to a file?

    - by Zka
    I have a simple program where I would like to save an arraylist to a file, so that when the program is restarted, it loads from the file to the arraylist in memory. Is this possible in C#? Or do I need to itterate over the arraylist countaining my custom classes and in someway print them out? Any tips on a correct way to do this?

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  • Java JCheckBox ArrayList help needed

    - by user2929626
    I'm new to Java and struggling with something which I'm sure must have a simple answer but I can't seem to find it. I have an array of checkbox objects defined as: ArrayList<JCheckBox> checkBoxList A JPanel is created with a grid layout and the checkboxes are added to the JPanel and the ArrayList: for (int i = 0; i < 256; i++) { JCheckBox c = new JCheckBox(); c.setSelected(false); checkBoxList.add(c); mainPanel.add(c); } Yes, there are 256 checkboxes! The panel is added to a JFrame and eventually the GUI is displayed. The user can select any combination of the 256 checkboxes. My class implements Serializable and this ArrayList of checkboxes can be saved and restored using 'Save' and 'Load' GUI buttons. My code to load the saved object is as below: public class LoadListener implements ActionListener { public void actionPerformed(ActionEvent a) { try { // Prompt the user for a load file JFileChooser fileLoad = new JFileChooser(); fileLoad.showOpenDialog(mainFrame); // Create a object/file input stream linking to the selected file ObjectInputStream is = new ObjectInputStream(new FileInputStream(fileLoad.getSelectedFile())); // Read the checkBox array list checkBoxList = (ArrayList<JCheckBox>) is.readObject(); is.close(); } catch (Exception ex) { ex.printStackTrace(); } } On loading the ArrayList object, the values of the checkboxes are correctly populated, however I want to update the checkboxes on the GUI to reflect this. Is there an easy way to do this? I assumed as the array of checkboxes had the correct values that I could just repaint the panel / frame but this doesn't work. I'd like to understand why - does my loaded array of checkbox objects no longer reflect the checkbox objects on the GUI? Any help would be much appreciated. Thanks!

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  • Arraylist is null; I cannot access books in the arraylist

    - by user3701380
    I am a beginner-intermediate java programmer and I am getting a null pointer exception from my arraylist. I am writing a bookstore program for APCS and when i add the book, it is supposed to add to the arraylist in the inventory class. But when i call a method to search for a book (e.g. by title), it shows that there isn't anything in the arraylist. //Here is my inventory class -- it has all methods for adding the book or searching for one The searching methods are in getBookByTitle, getBookByAuthor, and getBookByISBN and the method for adding a book is addBook package webbazonab; //Inventory Class //Bharath Senthil //Ansh Sikka import java.util.ArrayList; public class Inventory{ private ArrayList<Book> allBooks = new ArrayList<Book>(); private String bookTitles; private String bookAuthors; private String bookPrices; private String bookCopies; private String ISBNs; public Inventory() { } //@param double price, int copies, String bookTitle, String Author, String isbnNumber public void addBooks(Book addedBook){ allBooks.add(addedBook); } public boolean isAvailable(){ for(Book myBook : allBooks){ if(myBook.copiesLeft() == 0) return false; } return true; } public String populateTitle(){ for (Book titleBooks : allBooks){ bookTitles = titleBooks.getTitle() + "\n"; return bookTitles; } return bookTitles; } public String populateAuthor(){ for(Book authorBooks : allBooks){ bookAuthors = authorBooks.getAuthor() + "\n"; return bookAuthors; } return bookAuthors; } public String populatePrice(){ for (Book pricedBooks : allBooks){ bookPrices = String.valueOf(pricedBooks.getPrice()) + "\n"; } return "$" + bookPrices; } /** * * @return */ public String populateCopies(){ for (Book amtBooks : allBooks){ bookCopies = String.valueOf(amtBooks.copiesLeft()) + "\n"; return bookCopies; } return bookCopies; } public String populateISBN(){ for (Book isbnNums : allBooks){ ISBNs = isbnNums.getIsbn() + "\n"; return ISBNs; } return ISBNs; } @SuppressWarnings("empty-statement") public Book getBookByTitle(String titleSearch) { for(Book titleBook : allBooks) { if (titleBook.getTitle().equals(titleSearch)) { return titleBook; } } return null; } public Book getBookByISBN(String isbnSearch){ for(Book isbnBookSearches : allBooks){ if(isbnBookSearches.getIsbn().equals(isbnSearch)){ return isbnBookSearches; } } return null; } public Book getBookByAuthor(String authorSearch){ for(Book authorBookSearches : allBooks){ if(authorBookSearches.getAuthor().equals(authorSearch)){ return authorBookSearches; } } return null; } public void sort(){ for(int i = 0; i < allBooks.size(); i++) { for(int k = 0; k < allBooks.size(); k++) { if(((Book) allBooks.get(i)).getIsbn().compareTo(((Book) allBooks.get(k)).getIsbn()) < 1) { Book temp = (Book) allBooks.get(k); allBooks.set(k, allBooks.get(i)); allBooks.set(i, temp); } else if(((Book) allBooks.get(i)).getIsbn().compareTo(((Book) allBooks.get(k)).getIsbn()) > 1) { Book temp = (Book) allBooks.get(i); allBooks.set(i, allBooks.get(k)); allBooks.set(k, temp); } } } } public ArrayList<Book> getBooks(){ return allBooks; } } //The exception occurs when i call the method here (in another class): Inventory lib = new Inventory(); jTextField12.setText(lib.getBookByAuthor(authorSearch).getTitle()); Here is my book class if you need it package webbazonab; //Webbazon AB //Project By: Ansh Sikka and Bharath Senthil public class Book { private double myPrice; private String myTitle; private String bookAuthor; private String isbn; private int myCopies; public Book(double price, int copies, String bookTitle, String Author, String isbnNumber) { myPrice = price; myCopies = copies; myTitle = bookTitle; bookAuthor = Author; isbn = isbnNumber; } public double getPrice() { return myPrice; } public String getIsbn() { return isbn; } public String getTitle() { return myTitle; } public String getAuthor() { return bookAuthor; } public int copiesLeft(){ return myCopies; } public String notFound(){ return "The book you searched for could not be found!"; } public String toString() { return "Title: " + getTitle() + "\nAuthor: " + getAuthor() + "\nNumber of Available Books: " + copiesLeft() + "\nPrice: $" + getPrice(); } } Thanks!

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  • How do I make my ArrayList Thread-Safe? Another approach to problem in Java?

    - by thechiman
    I have an ArrayList that I want to use to hold RaceCar objects that extend the Thread class as soon as they are finished executing. A class, called Race, handles this ArrayList using a callback method that the RaceCar object calls when it is finished executing. The callback method, addFinisher(RaceCar finisher), adds the RaceCar object to the ArrayList. This is supposed to give the order in which the Threads finish executing. I know that ArrayList isn't synchronized and thus isn't thread-safe. I tried using the Collections.synchronizedCollection(c Collection) method by passing in a new ArrayList and assigning the returned Collection to an ArrayList. However, this gives me a compiler error: Race.java:41: incompatible types found : java.util.Collection required: java.util.ArrayList finishingOrder = Collections.synchronizedCollection(new ArrayList(numberOfRaceCars)); Here is the relevant code: public class Race implements RaceListener { private Thread[] racers; private ArrayList finishingOrder; //Make an ArrayList to hold RaceCar objects to determine winners finishingOrder = Collections.synchronizedCollection(new ArrayList(numberOfRaceCars)); //Fill array with RaceCar objects for(int i=0; i<numberOfRaceCars; i++) { racers[i] = new RaceCar(laps, inputs[i]); //Add this as a RaceListener to each RaceCar ((RaceCar) racers[i]).addRaceListener(this); } //Implement the one method in the RaceListener interface public void addFinisher(RaceCar finisher) { finishingOrder.add(finisher); } What I need to know is, am I using a correct approach and if not, what should I use to make my code thread-safe? Thanks for the help!

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  • java: <identifier> expected with ArrayList

    - by A-moc
    I have a class named Storage. Storage contains an arraylist of special objects called Products. Each product contains information such as name, price, etc. My code is as follows: class Storage{ Product sprite = new Product("sprite",1.25,30); Product pepsi = new Product("pepsi",1.85,45); Product orange = new Product("orange",2.25,36); Product hershey = new Product("hershey",1.50,33); Product brownie = new Product("brownie",2.30,41); Product apple = new Product("apple",2.00,15); Product crackers = new Product("peanut",3.90,68); Product trailmix = new Product("trailmix",1.90,45); Product icecream = new Product("icecream",1.65,28); Product doughnut = new Product("doughnut",2.75,18); Product banana = new Product("banana",1.25,32); Product coffee = new Product("coffee",1.30,40); Product chips = new Product("chips",1.70,35); ArrayList<Product> arl = new ArrayList<Product>(); //add initial elements to arraylist arl.add(sprite); arl.add(pepsi); arl.add(orange); arl.add(hershey); arl.add(brownie); arl.add(apple); arl.add(peanut); arl.add(trailmix); arl.add(icecream); arl.add(doughnut); arl.add(banana); arl.add(coffee); arl.add(chips); } Whenever I compile, I get an error message on lines 141-153 stating <identifier> expected. I know it's an elementary problem, but I can't seem to figure this out. Any help is much appreciated.

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  • Android Java ArrayList inserting element not working

    - by DavidNg
    I have a simple Android program with one button and one textview. When the button is clicked, a number is inserted in in an ArrayList. However, it does not work. If changing to add, it works fine. package test_ad.com; import java.util.ArrayList; import android.app.Activity; import android.os.Bundle; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.TextView; public class Test_adActivity extends Activity { ArrayList<Integer> al = new ArrayList<Integer>(); Button myB; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); myB = (Button) findViewById(R.id.button1); myTV = (TextView) findViewById(R.id.textView1); myB.setOnClickListener(new OnClickListener() { public void onClick(View arg0) { al.set(i,10*i);//insert an Integer at index i, but not working i++; if (i == 5) myTV.setText(al.toString()); } }); } }

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  • get Random in ArrayList has error of java.lang.IllegalArgumentException: n must be positive

    - by gabrielle fregil
    In my ArrayList, i have get a random Item from my ArrayList for the equip method. Whenever i use my tester, the terminal window prints java.lang.IllegalArgumentException: n must be positive when I try to call random for the size. I tried to change the value of totalElements to the integer size of the elements, then the error would be an OutOfBoundsExeption import java.util.*; import java.util.Scanner; import java.util.Random; public class GameMaster { private int turn, totalElements; private boolean winner; private Avatar x1; private Avatar x2; private ArrayList<Item> inventory; public GameMaster(Avatar a1, Avatar a2) { x2 = a1; x1 = a2; turn = 1; winner = false; inventory = new ArrayList<Item>(); totalElements = 0; } private void fillInventory() { inventory.add( new Item( "Zealot Blades", true, 8 ) ); inventory.add( new Item( "BFG", true, 13 ) ); inventory.add( new Item( "Synthetic Cloth", false, 7 ) ); // more items inventory.add( new Item( "Gauss Rifle", true, 9 ) ); inventory.add( new Item( "Flight Unit", false, 6 ) ); totalElements = inventory.size(); } public String equip() { Avatar w; String a; if (turn%2==1) w=x2; else w=x1; if (w.beltIsFull()) { a = w.getName() + "'s belt is full. \n"; } else { turn++; Random generator = new Random(); Item rand = inventory.get(generator.nextInt(totalElements)); //terminal window in blueJ: java.lang.IllegalArgumentException: n must be positive a = w.getName()+" is equiped with "+rand.getName()+"."; } return a; }

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  • Having trouble binding a ksoap object to an ArrayList in Android

    - by Maskau
    I'm working on an app that calls a web service, then the webservice returns an array list. My problem is I am having trouble getting the data into the ArrayList and then displaying in a ListView. Any ideas what I am doing wrong? I know for a fact the web service returns an ArrayList. Everything seems to be working fine, just no data in the ListView or the ArrayList.....Thanks in advance! EDIT: So I added more code to the catch block of run() and now it's returning "org.ksoap2.serialization.SoapObject".....no more no less....and I am even more confused now... package com.maskau; import java.util.ArrayList; import org.ksoap2.SoapEnvelope; import org.ksoap2.serialization.PropertyInfo; import org.ksoap2.serialization.SoapObject; import org.ksoap2.serialization.SoapSerializationEnvelope; import org.ksoap2.transport.AndroidHttpTransport; import android.app.*; import android.os.*; import android.widget.ArrayAdapter; import android.widget.Button; import android.widget.EditText; import android.widget.ListView; import android.widget.TextView; import android.view.View; import android.view.View.OnClickListener; public class Home extends Activity implements Runnable{ /** Called when the activity is first created. */ public static final String SOAP_ACTION = "http://bb.mcrcog.com/GetArtist"; public static final String METHOD_NAME = "GetArtist"; public static final String NAMESPACE = "http://bb.mcrcog.com"; public static final String URL = "http://bb.mcrcog.com/karaoke/service.asmx"; String wt; public static ProgressDialog pd; TextView text1; ListView lv; static EditText myEditText; static Button but; private ArrayList<String> Artist_Result = new ArrayList<String>(); @Override public void onCreate(Bundle icicle) { super.onCreate(icicle); setContentView(R.layout.main); myEditText = (EditText)findViewById(R.id.myEditText); text1 = (TextView)findViewById(R.id.text1); lv = (ListView)findViewById(R.id.lv); but = (Button)findViewById(R.id.but); but.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { wt = ("Searching for " + myEditText.getText().toString()); text1.setText(""); pd = ProgressDialog.show(Home.this, "Working...", wt , true, false); Thread thread = new Thread(Home.this); thread.start(); } } ); } public void run() { try { SoapObject request = new SoapObject(NAMESPACE, METHOD_NAME); PropertyInfo pi = new PropertyInfo(); pi.setName("ArtistQuery"); pi.setValue(Home.myEditText.getText().toString()); request.addProperty(pi); SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER11); envelope.dotNet = true; envelope.setOutputSoapObject(request); AndroidHttpTransport at = new AndroidHttpTransport(URL); at.call(SOAP_ACTION, envelope); java.util.Vector<Object> rs = (java.util.Vector<Object>)envelope.getResponse(); if (rs != null) { for (Object cs : rs) { Artist_Result.add(cs.toString()); } } } catch (Exception e) { // Added this line, throws "org.ksoap2.serialization.SoapObject" when run Artist_Result.add(e.getMessage()); } handler.sendEmptyMessage(0); } private Handler handler = new Handler() { @Override public void handleMessage(Message msg) { ArrayAdapter<String> aa; aa = new ArrayAdapter<String>(Home.this, android.R.layout.simple_list_item_1, Artist_Result); lv.setAdapter(aa); try { if (Artist_Result.isEmpty()) { text1.setText("No Results"); } else { text1.setText("Complete"); myEditText.setText("Search Artist"); } } catch(Exception e) { text1.setText(e.getMessage()); } aa.notifyDataSetChanged(); pd.dismiss(); } }; }

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  • Arraylist as repeater datasource (how to access from .aspx)

    - by Phil
    I have an arraylist: Dim downloadsarray As New ArrayList downloadsarray.Add(iconlink) downloadsarray.Add(imgpath) downloadsarray.Add(filesize) downloadsarray.Add(description) Which is the datasource of my repeater: DownloadsRepeater.DataSource = downloadsarray DownloadsRepeater.DataBind() Please can you tell me how I output the items in the array to the .aspx page. I usually use (when using sqldatareader as datasource): <%#Container.DataItem("1stcolumnnamestring")%> <%#Container.DataItem("2ndcolumnnamestring")%> But this does not work when using the arraylist as datasource. Thanks. ps... I know how to use <%#Container.DataItem% to dump everything but I need to get at the items in the array individually, not have them all ditched out to the page in one go. For example, item 1 contains a link, item 2 contains an image path, item 3 contains a description. I need to have them kick out in the correct order to build the link and icon correctly.

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  • Arraylist can't compare objects after they are loaded from disk

    - by Zka
    To make it easy, lets say I have an arraylist allBooks containing class "books" and an arraylist someBooks containing some but not all of the "books". Using contains() method worked fine when I wanted to see if a book from one arraylist was also contained in another. The problem was that this isn't working anymore when I save both of the Arraylists to a .bin file and load them back once the program restarts. Doing the same test as before, the contains() returns false even if the compared objects are the same (have the same info inside). I solved it by overloading the equals method and it works fine, but I want to know why did this happen?

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  • C# arraylist can't compare objects after they are loaded from disk

    - by Zka
    To make it easy, lets say I have an arraylist allBooks containing class "books" and an arraylist someBooks containing some but not all of the "books". Using contains() method worked fine when I wanted to see if a book from one arraylist was also contained in another. The problem was that this isn't working anymore when I save both of the Arraylists to a .bin file and load them back once the program restarts. Doing the same test as before, the contains() returns false even if the compared objects are the same (have the same info inside). I solved it by overloading the equals method and it works fine, but I want to know why did this happen?

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  • set arraylist element as null

    - by Jessy
    The first index is set to null (empty), but it doesn't print the right output, why? //set the first index as null and the rest as "High" String a []= {null,"High","High","High","High","High"}; //add array to arraylist ArrayList<Object> choice = new ArrayList<Object>(Arrays.asList(a)); for(int i=0; i<choice.size(); i++){ if(i==0){ if(choice.get(0).equals(null)) System.out.println("I am empty"); //it doesn't print this output } }

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