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How to access array from different activity?

Yes I'm really new to android and I'm wokring on a very simple app.
On my mainActivity I'm creating and array, and want to access the array from a different activity.
public class Activity extends {
MyAreas[] myArea;
#Override
protected void onCreate(Bundle savedInstanceState) {
myArea= new MyAreas[2];
myArea[0] = new MyAreas(33, 44, "Location ", "active");
myArea[1] = new MyAreas(32, 434, "Location 2", "active");
Class
public class MyAreas{
public double val;
public double val2;
public String name;
public String status;
public MyAreas(double val, double val2, String name, String status) {
this.val= val;
this.val2= val2;
this.name = name;
this.status = status;
}
I'm trying to access myarea array from my activity2.java, I tried this but didn't work.
private ArrayList<MyAreas> mMyAreasList;

Using Parcelable to pass data between Activity
Here is answer which should help.

In regular Java you can use getters to obtain objects or any variable from a different class. Here is a good article on encapsulation.
In Android, there is a class called Intent that lets you start one activity from another and pass any necessary information to it. Take a look at the developer docs and this other answer which should help you.

For your begginer level, rather than using intents, just set the array object public and static, like that:
public static MyAreas[] myArea;
By that way you can access it from any activity in your app..
Then, go to the activity2.java wherever you want to access it.
MyAreas area = Activity.myArea[0];

The problem with this approach is that you do not have complete control when and in what order the activities are created or destroyed. Activities are sometimes destroyed and automatically restarted in response to some events. So it may happen that the second activity is started before the first activity, and the data is not initialized. For this reason it is not a good idea to use static variables initialized by another activity.
The best approach is to pass the data via the intent. The intents are preserved across activity restarts, so the data will be preserved as well.
Another approach is to have a static field to keep the data, and initialize the data in an Application instance.

global variables between different classes java

i am on the creation of an app in android. its a calculator app. the main activity is where the user could input the equation, and the second activity is where the user can add/edit/delete variables. so i made a new class in another file named Global.java. then i extended it to application, imported everything i need, made s private string, made some public functions, edited the manifest, and initialized it right on my main activity. everything works fine while im only using a string to be passed by the functions but when i started adding what i need, an ArrayList, and made some functions so i could access the list then run it, the app closes. i think its because the arraylist is not allowed to be passed to different classes? am i right or am i just missing something?
please dont downvote my post if i didn't post something needed. i am using aide so there is no log output. code:
Global.java
...
import android.app.*;
import java.util.*;
public class Global extends Application
{
private String s;
public static ArrayList<String> sList;
public String getS() {
return s;
}
public void setS(String ss) {
s=ss;
}
public void add() {
sList.add(s);
}
}
MainActivity.java
...
String s;
...
global=(Global)getApplicationContext();
...
global.setS("jian"); //this one works
global.sList.add("jian"); // this one dont
...

Are you sure you initialized sList, like this:
sList = new ArrayList<String>();
If you didn't, you might want to change its declaration to include this initialization.
public static ArrayList<String> sList = new ArrayList<String>();

Just do
global.add("jian");
since you have an add function to take care of the addition of item to arraylist.
Also, try with this:
public void add(String ss) {
sList.add(ss);
}

You are not instantiating your arraylist.
public static ArrayList<String> sList = new Arraylist<String>();
Also you should read beginner tutorials on Java and android, using a public extension of application like this is a bad idea and you can get log outputs from different apps if Aide doesn't provide that, search play store

Android message between classes

This is my first post and I did not find anything similar, so I've decided to ask.
Im developing a Poker Game for Android to practice the SDK and refresh/improve my Java. Its a simple app that control a texas hold'em poker hand.
Initally, I wrote my classes using only Java SE and it looks fine. Each class has its own purpose and testing it with console input/output, I can see it really works :)
Last week, I decided to port it to Android to see things happening through a graphic interface, so I got the resource images, make an Activity and included my poker package.
Before port to Android I can just put a println (or readLine) to see whats going on and send my inputs. Now Im stuck in how each class can communicate to the game activity to provide what must be drawn. If possible, I don't want insert Android draw code inside game classes. Im trying find a way to exchange messages between my Activity and the game classes and Id like some suggetions. Im new in developing Android apps, so I dont know all mechanics to do this.
Below are the snippet from my activity:
package my.poker.game;
//import stuff
public class ActivityHand extends Activity
{
private static Vector<Player> Players = new Vector<Player>();
public static final int MAX_PLAYERS = 8;
public static void startEmptyTable()
{
Players.removeAllElements();
Players.setSize(MAX_PLAYERS);
}
public static void LeaveTable(int pos)
{
Players.set(pos, null);
}
public static void SitTable(int pos, Player player)
{
Players.set(pos, player);
}
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
int cash = 1000;
startEmptyTable();
SitTable(0, new Jogador("William", cash));
SitTable(2, new Jogador("Richard", cash));
SitTable(4, new Jogador("John", cash));
SitTable(6, new Jogador("Paul", cash));
SitTable(8, new Jogador("Albert", cash));
//Start a Hand.... in future this will be a loop for each Hand
Hand hand = new Hand(Players);
}
}
The object hand, will select a Dealer, deal the cards, control the small and big blinds and start the game loop.
The question is: how the hand class can tell the Activity to Draw and pass an object containing what to draw?
Thanks a lot for your help
Editing: I've decided to try implementing it using a Handler and passing simple messages. As I read from Handler at Developers a Handler object is assigned to thread's MessageQueue, so I tried to put this into my Activity Class (before Hand hand = new Hand (...) ):
Handler handler = new Handler()
{
#Override
public void handleMessage(Message msg)
{
Bundle bundle = msg.getData();
// Do something with message contents
}
};
And inside the Hand class I put this when I want to draw something:
Handler handler = new Handler();
Message msg = new Message();
Bundle bundle = new Bundle();
bundle.putString("Key", "The Key's Value");
msg.setData(bundle);
handler.sendMessage(msg);
As I understood, both handlers are from same thread, so they are assigned to same MessageQueue right? I tought when I send a message inside Hand class, the Activity class can receive it in handleMessage method and processes any message I send, but handleMessage doesn't execute.
What am I missing?
Thanks again

To call methods in the activity, you want to pass the activity to this class.
for example:
public class PokerActivity extends Activity
{
#Override
public void onCreate(Bundle savedInstanceState)
{
Hand hand = new Hand(this);
}
public void setVisibleHand(Player player)
{
<do something in the activity>
}
}
public class Hand
{
PokerActivity pokerActivity;
public Hand(PokerActivity activity)
{
this.pokerActivity = activity;
}
public void setVisibleHand()
{
pokerActivity.setVisibleHand(player1);
}
}
Now, this might not be the best way to do it. In Android you have to be carefull to not leak the context, or you might be getting trouble with the memory. (simply passing the activity/context might be the easy way, but is also the easiest way to leak the context.)
I'd advise you to look at some simple tutorials first, to get a feeling of how android activities work.

You could use a Handler and Message system to communicate between your classes.
This tutorial by Lars Vogel should help you Android Threads, Handlers and AsyncTask - Tutorial

You will have to create another class to make the interactions with your own classes and the activity itself.
From that class you can use the activity context to control the android activity.
The approach about using Handlers and Messages is good but would require you to modify your game classes.

Maybe you should extend View Class to draw the Hand.
http://developer.android.com/reference/android/view/View.html

How to pass a custom class between Activities

I found many simple solutions to this (such as Intent.putExtra(String, String) and Bundle.putString(String, String)), but this is not helpful for my situation.
I have a class called MyMP3 which contains non-primitive types. I need to pass the following for MyMP3...
private AudioFile audioFile;
private Tag tag;
private int index;
private boolean saved, startedWithLyrics;
private String id3lyrics;
AudioFile and Tag are both classes that I imported from a .jar file. How can I go about passing these to another Activity via Intents? I tried messing with implementing Parcelable for my "MyMP3" class, but I am not sure how to correctly use these methods when not passing primitive types.
Could you help me out and look at my code below and try to tell me how to correctly use Parcelable with a custom class like mine? How do I set the Parcel in the writeToParcel function and how do I correctly retrieve the class in another Activity?
Below is my code (the part that is important, at least). I've been trying different things for a couple of days now, but I cannot get it to work. Please help me out!
public class MyMP3 extends AudioFile implements Parcelable
{
private AudioFile audioFile;
private Tag tag;
private int index;
private boolean saved, startedWithLyrics;
private String id3lyrics;
public MyMP3(File f, int index)
{
this.audioFile = AudioFileIO.read(f);
this.tag = this.audioFile.getTag();
this.index = index;
this.saved = false;
this.id3lyrics = getLyrics();
}
#Override
public int describeContents()
{
return 0;
}
#Override
public void writeToParcel(Parcel out, int flats)
{
/* This method does not work, but I do not know how else to implement it */
Object objects[] = {this.audioFile, this.tag, this.index, this.saved, this.startedWithLyrics, this.id3lyrics};
out.writeArray(objects);
}
public static final Parcelable.Creator<MyMP3> CREATOR = new Parcelable.Creator<MyMP3>()
{
public MyMP3 createFromParcel(Parcel in)
{
/* Taken from the Android Developer website */
return new MyMP3(in);
}
public MyMP3[] newArray(int size)
{
/* Taken from the Android Developer website */
return new MyMP3[size];
}
};
private MyMP3(Parcel in)
{
/* This method probable needs changed as well */
Object objects[] = in.readArray(MyMP3.class.getClassLoader());
}
}

You can make your MyMP3 class Parcelable like that. Make sure you get the read/write order correct. The non-primitives must also be Parcelable, so you might not have control over that unfortunately. Alternatively, you could come up with your own serialization/deserialization. You could use a text format, like JSON or XML. Another alternative is to use subclass Application (make sure you declare it in your manifest) and use it is as a place to hang objects that span Activities. This keeps the object in memory for the lifecycle of your app, so be careful with doing this.

Passing a String Array Between Java Classes Android App

I am writing an Android app where I need to pass a string array between two classes. The string initializes fine and I can output the contents of the string fine in the one class but as I try to pass it to another class I get a Null Pointer Exception error. The following is the stripped down version of my code:
accelerometer.java:
public class accelerometer extends Service {
public String movement[];
public void onCreate() {
movement = new String[1000000];
}
public void updatearray() {
movement[arraypos]=getCurrentTimeString();
//Toast.makeText(this, movement[arraypos] , Toast.LENGTH_SHORT).show(); //this correctly displays each position in the array every time it updates so I know the array is working correctly in this file
arraypos+=1;
}
public String[] getmovement(){
return movement;
}
}
wakeupalarm.java:
public class wakeupalarm extends Activity {
private TextView herestext_;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.wakeup);
herestext_ = (TextView) findViewById(R.id.TextView01);
accelerometer accelerometercall = new accelerometer();
String movearray[] = accelerometercall.getmovement();
herestext_.setText(movearray[2]);
}
}
I have a feeling I'm missing something very simple but any help would be greatly appreciated!
Thanks,
Scott

You're creating a new accelerometer class, which is completely uninitialized since there is no constructor, then you access its member. Of course it'll be null.
Not sure how your two classes are related, but if the activity is called by the service, then you need to pass the string through the intent (through an extra, for example).
Side note: Class names should always start with a capital letter. Method/variable names should have camel case, i.e. "updateArray". Also, you can format your code here by selecting it and pressing CTRL+K.

Your first problem, I think, is that you are creating an array with a million slots in it. Do you really mean to be doing that? It's going to take a lot of memory---quite possibly more than is available. You should instead look to having a Vector of Strings that you extend as necessary.