How to access a String array initialized in one method from another method?

Question

I have a simple requirement I have a String array which I declare at the class level so that I can use it anywhere in the class.

 String image_url[];//Declared outside of any methods

//Initailzed image_url[] to img_url[]
public void showJSON(String json)
    {
        ParseJSON pj =  new ParseJSON(json);
        pj.parseJSON();

        image_url= ParseJSON.img_url;
Toast.makeText(DisplayMagazine.this, "Image loc"+image_url[1], Toast.LENGTH_SHORT).show();
    }

I want to use the image_url array in the following method as:-

 private ArrayList prepareData() {


        ArrayList android_version = new ArrayList<>();

        for (int i = 0; i < magazine_version_names.length; i++) {
            MagazineVersion magazineVersion = new MagazineVersion();
            magazineVersion.setMagazine_version_name(magazine_version_names[i]);
            magazineVersion.setMagazine_image_url(image_url[i]);
            android_version.add(magazineVersion);
        }
        return android_version;
    }

When I run this code the app crash's with a null pointer exception at this line:-

magazineVersion.setMagazine_image_url(image_url[i]);

This is the code for ParseJSON:-

public class ParseJSON
{
    public static String[] magversion;
    public static String[] img_url;
    public static String[] download_url;
    public static String[] sample_url;
    public static String[] status_dl;
    public static String[] status_sm;
    public static String[] device_id;

    public static final String JSON_ARRAY = "result";
    public static final String KEY_MAGVER = "magversion";
    public static final String KEY_IMGURL = "img_url";
    public static final String KEY_DOWNLOADURL = "download_url";
    public static final String KEY_SAMPLEURL = "sample_url";
    public static final String KEY_STATUS_DL ="status_dl";
    public static final String KEY_DEVICE_ID ="device_id";

    private JSONArray magazines = null;

    private String json;

    public ParseJSON(String json){
        this.json = json;
    }

    public void parseJSON(){
        JSONObject jsonObject=null;
        try {
            jsonObject = new JSONObject(json);
            magazines = jsonObject.getJSONArray(JSON_ARRAY);

            magversion = new String[magazines.length()];
            img_url = new String[magazines.length()];
            download_url = new String[magazines.length()];
            sample_url= new String[magazines.length()];
            status_dl= new String[magazines.length()];
            device_id= new String[magazines.length()];

            for(int i=0;i<magazines.length();i++){
                JSONObject jo = magazines.getJSONObject(i);
                magversion[i] = jo.getString(KEY_MAGVER);
                img_url[i] = jo.getString(KEY_IMGURL);
                download_url[i] = jo.getString(KEY_DOWNLOADURL);
                sample_url[i] = jo.getString(KEY_SAMPLEURL);
                status_dl[i] = jo.getString(KEY_STATUS_DL);
                device_id[i] = jo.getString(KEY_DEVICE_ID);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
    }

}

I am new to programming so any help or suggestion is appreciated.Thank you.

Possible duplicate of [What is a NullPointerException, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — OH GOD SPIDERS, Jul 28 '16 at 11:36
Hint: understanding what fields are, and how they relate to your classes is **absolute essential basic** stuff. If you don't know about such things, you better keep your fingers away from android programming. For now. The point is: don't try to learn java doing android programming. First learn java basics, then turn to Android. Anything else will cause a (probably short) series of very frustrating "why this not worky" experiences for you. Short, because you will soon run out of motivation. — GhostCat, Jul 28 '16 at 11:37
@JordiCastilla please check my updated question I have added the ParseJson class this is what my constructor looks like :- public ParseJSON(String json){ this.json = json; } — anup, Jul 28 '16 at 11:44

score 1 · Answer 1 · answered Jul 28 '16 at 11:48

You Array is not initialized so I think that's why its giving null pointer exception. Try to debug that why array is null. Code snippet below help you to execute the scenario.

public class Abc {

    String image_url[];

    public void abc(){
        image_url = new String[] {"10","20","30"};
    }       

    public static void main(String[] args) {

        Abc a = new Abc();
        a.abc();
        System.out.println(a.image_url[0]+" "+a.image_url[1]+" "+a.image_url[2]);
    }
//OutPut - 10 20 30 
}

score 0 · Answer 2 · answered Jul 28 '16 at 11:38

0

Your array is null and if you try to access an element of null array, it will throw a null pointer not an ArrayOutOfBound.

answered Jul 28 '16 at 11:38

Rupesh

338
7
19

score 0 · Answer 3 · answered Jul 28 '16 at 11:55

0

We need to see the calling code, order of calls is important in your case!

Are you sure you are calling prepareData() after calling showJSON(), not before?

answered Jul 28 '16 at 11:55

M-Zaiady

136
9

How to access a String array initialized in one method from another method?

3 Answers3