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ArrayList troubles

I was wondering how to reference an ArrayList a different method than it was declared in.
For example I am writing a program that allows me to create a playlist of songs, so in one method I have createAPlaylist and then another method I have shuffle().
In my playlist method I have created an ArrayList but I am having trouble using this arrayList in my shuffle method. There is some code below for context:
public static void createAPlaylist() {
try {
System.out.println("We have the following tracks:");
ArrayList<String> songs = new ArrayList<String>();
String firstSong = jukebox.allTracks.get(0).getTitle();
songs.add(firstSong);
for (int index = 0; index < count; index++) {
System.out.println(SPACES + (index + 1) + ". " + jukebox.allTracks.get(index).getTitle());
}
System.out.println("Select a track to add to the playlist: ");
int songNumber = input.nextInt();
String songSelected = songs.get(songNumber);
songs.add(songSelected);
input.nextLine();
} catch (Exception e) {
System.out.println("\nplease select a valid song number.");
}
}

This is what method parameters are for:
public static void createAPlaylist() {
ArrayList<String> songs = new ArrayList<>();
shuffle(songs);
}
public static void shuffle(ArrayList<String> songs) {
// Do stuff with your ArrayList here
}

You can the arraylist from the createAPlaylist method and pass that to shuffle method:
Like:
public static List<String> createAPlaylist() {
...
...
...
return songs;
}
/// and then in shuffle method receive that as parameter :
public static void shuffle(List<String> songs){
// access that songs list by
}
Or you could:
Instead of method variable declare that arraylist as class variable..
Like:
public class ClassName{
public static ArrayList<String> songs = new ArrayList<String>();
public static void createAPlaylist() {
...
...
...
// reset the songs.
songs = new ArrayList<String>();
...
}
/// and then in another method:
public static void suffle(){
// access that songs list by
List<String> createdSongs = ClassName.songs;
}

In Java, variables are only available within the context they are created - so if you create an ArrayList inside a method, you cannot access it outside of that method unless you store it in the method’s class, or you return the variable from the method it’s made it.
You can either declare the ArrayList outside of the method, as a class field, like so:
public class Foo {
private static ArrayList<String> arrayList = new ArrayList<String>();
public static void createAPlaylist() {
arrayList.add();
etc...
}
}
Or you could return the ArrayList from the method like so:
public class Foo {
public static void main(String[] args) {
ArrayList<String> arrayList = createAPlaylist();
}
public static ArrayList<String> createAPlaylist() {
ArrayList<String> songs = new ArrayList<String>();
// Your code here
// Note that you have to return the list from
// inside the catch block!
// I’d recommend creating the ‘songs’ ArrayList
// outside of the ‘try’ block, so that you can
// have a fallback if something fails in the ‘try’
return songs;
}
}
I don’t know if you intend to have this all static. I’d think it will work better as non static, but that’s a matter for another question, so I’ve left it as-is in the examples.
Sorry if this isn’t formatted perfectly - I’m on a mobile device and don’t have my IDE.

Tester class doesn't think my ArrayList is an ArrayList

I'm trying to create an ArrayList of type Item in my Store class and then test it in another class called StoreTester. I keep getting the error: The method get() is undefined for the type Store. So Java thinks my tester object of type Store is not an ArrayList even though I tried to make it so.
My Store class constructor:
import java.util.ArrayList;
public class Store
{
private ArrayList<Item> blockbuster;
public Store(){
blockbuster = new ArrayList<Item>();
}
public void addItem(Item i){
blockbuster.add(i);
}
}
This is my StoreTester class:
import java.util.ArrayList;
public class StoreTester{
public static void main(String[] args){
Store videostore = new Store();
System.out.print(videostore.toString());
System.out.print(videostore.get(0));
}
}
For some reason videostore.toString() works fine and prints out the list of objects I've added to it. Here is the method toString I wrote in my Store class:
public String toString(){
String item = "Items in store: " + "\n";
for(int j = 0; j < blockbuster.size(); j++){
item = item + blockbuster.get(j).getTitle() + "\n";
}
return item;
}
but as soon as I try to get() a specific object at an index or even use videostore.size(), i get the: method undefined error. Hopefully it is just a syntax error or something simple I've overlooked. Any help is appreciated.

Yes, Store does not have a method get
It can be implemented in Store as
public Item get (int index) {
// check for null, then
return blockbuster.get(index);
}
Store has-a ArrayList it is not Store is-a ArrayList
As #ElliottFrisch also mentions, you will need to implement a size method as well
public int size () {
// check for null, then
return blockbuster.size();
}

How can I assign instance of a class from an array to a class initializer in java?

In a Android application I am making I have an array of instances of a certain class I made, and later in the program I need to use the getter and setter methods from that class on an instance of the class from the array. Do I need to assign the instance of the class from the array to a new class initializer? Here is some code to clear this up:
Class
public class ProfileInformation {
private String console;
private String gamertag;
public String getConsole() {
return console;
}
public void setConsole(String console) {
this.console = console;
}
public String getGamertag() {
return gamertag;
}
public void setGamertag(String gamertag) {
this.gamertag = gamertag;
}
}
Array
ArrayList<ProfileInformation> ProfTags = new ArrayList<>();
Some instances of ProfileInformation are then added to arraylist, and then I get one of the instances from the arraylist and try to use getGamertag() to set it to a string:
ProfileInformation profNew = ProfTags.get(ProfTags.size()-1);
String example = profNew.getGamertag();
The problem is example will equal null. Why is this?

First, an Arraylist is a List, try not to confuse that with actual arrays.
Do I need to assign the instance of the class from the array to a new class initializer?
You don't need to get an element out of the Arraylist, no. You can chain many methods together
String example = ProfTags.get(ProfTags.size()-1).getGamertag();
example will equal null. Why is this?
For the same reason any object is null... You never set it equal to anything else

This code runs on my laptop:
public static void main(String[] args) {
ArrayList<ProfileInformation> ProfTags = new ArrayList<>();
element = new ProfileInformation();
element.setGamertag("Actual Gamer tag value");
ProfTags.add(element);
ProfileInformation profNew = ProfTags.get(ProfTags.size()-1);
String example = profNew.getGamertag();
}
Output is:
Actual Gamer tag value
I guess you didn't call setGamertag(String).

java add object to arrayList

I read most of the other things on SO and I couldn't seem to find an answer.
Don't know how to write an add method. I'm getting a StackOverflowError. It seems to run infinitely which I am not sure why.
Also, just wanted to confirm that it is possible to write a print function that prints out everything in arraylist myPolygon right?
class IrregularPolygon{
private ArrayList <Point2D.Double> myPolygon;
// constructors
public IrregularPolygon() { }
// public methods
public void add(Point2D.Double aPoint) {
//System.out.println("in");
this.add(aPoint);
System.out.println("finished");
// for (Point2D.Double number : myPolygon) {
// System.out.println("Number = " + aPoint);
// }
}
}
public class App{
public static void main(String[] args){
IrregularPolygon polygon = new IrregularPolygon();
Point2D.Double point = new Point2D.Double(1.2, 2.3);
System.out.println(point);
polygon.add(point);
} // main
} // class

Calling this.add(aPoint) in add is a recursive call. This method calls itself, and there is no base case, so this results in a StackOverflowError once it recurses deeply enough.
It looks like you want to add it to the ArrayList, so change
this.add(aPoint);
to
myPolygon.add(aPoint);
In addition, you never initialized myPolygon, so it's null. Initialize it:
private ArrayList <Point2D.Double> myPolygon = new ArrayList<>();

Sencha: Iterating a list store of a custom BaseModel subclass

I just started playing with Sencha's Ext GWT yesterday and I've hit a wall. I combined methods from their JSON loaded grid and their editable grid. As a test data set I'm using a list of Stargate Atlantis episodes hence the SGAEpisode which is defined as:
public class SGAEpisode extends BaseModel {
public SGAEpisode() {
}
public SGAEpisode(String season, String episode) {
set("season",season);
set("episode",episode);
}
public void setSeason(String season) {
set("season",season);
}
public String getSeason(){
return get("season");
}
public void setEpisode(String name) {
set("episode",name);
}
public String getEpisode() {
return get("episode");
}
public String toString() {
return "Season: " + get("season") + " episode: " + get("episode");
}
}
the onModuleLoad() starts off with...
ModelType type = new ModelType();
type.setRoot("seasons");
type.addField("Season","season");
type.addField("Episode","episode");
String path = GWT.getHostPageBaseURL() + "senchaapp/sgaepisodes";
final RequestBuilder builder = new RequestBuilder(RequestBuilder.GET,path);
final MVProxy<String> proxy = new SProxy<String>(builder);
JsonLoadResultReader<ListLoadResult<SGAEpisode>> reader = new JsonLoadResultReader<ListLoadResult<SGAEpisode>>(type);
final BaseListLoader<ListLoadResult<SGAEpisode>> loader = new BaseListLoader<ListLoadResult<SGAEpisode>>(proxy,reader);
final ListStore<SGAEpisode> episodes = new ListStore<SGAEpisode>(loader);
so loader.load() works great, populating a grid, I can edit fields, but I don't see commitChanges() doing anything and I can't iterate over the ListStore "episodes" to gather changed or added values. Oh, and SProxy is just a DataProxy subclass to allow me to specify the season's JSON I'm loading into the grid.
If I try either
for(SGAEpisode episode : episodes) {
save(episode);
}
or
for(int i = 0; i < episodes.getCount(); i++) {
save(episodes.getAt(i));
}
I get an exception with the message "com.extjs.gxt.ui.client.data.BaseModel cannot be cast to com.mvsc.sencha.shared.SGAEpisode" Any idea what I'm doing wrong? Everything up to that point was defined/populated with SGAEpisodes.....
Addendum
Ok, so if I try
List<Record> modified = episodes.getModifiedRecords();
for(Record r : modified) {
ModelData md = r.getModel();
save(md.get("season"),md.get("episode"));
}
I can iterate, and get the modified values, but what's the point of having a ModelData subclass if I have to use the base class like this. Which makes me think I don't in fact have to..... little help?
Addendum 2 I tried subclassing BaseModelData instead with no success.

I know its an older post, I had the same issue. This is how I fixed it.
try iterating through the models in listStore.
for(SGAEpisode episode : episodes.getModels()) {
save(episode);
}