initializing array adapter and listarray error null pointer

Question

I don't understand what is happening

 public class MainActivity extends Activity {

    ArrayAdapter<String> aa;
    ArrayList<ArrayList<String>> l=null;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        place = (AutoCompleteTextView)findViewById(R.id.place);
        aa=new ArrayAdapter<String(getBaseContext(),android.R.layout.simple_list_item_1,l.get(0) );
        place.setAdapter(aa);
    }
}

But creating the new ArrayAdapter instance is causing runtime error due to java.lang.NullPointerExeption. I don't understand why and how can I fix this :-/

Your adapter ArrayList is null before given to adapter please initialize this variable. — Hareshkumar Chhelana
– Hareshkumar Chhelana, Commented Aug 5, 2014 at 4:17
you defined ArrayList but you didn't initialized it so you are getting NPE error. — Zafer Celaloglu
– Zafer Celaloglu, Commented Aug 5, 2014 at 5:35

Illegal Argument · Accepted Answer · 2014-08-05 03:34:09Z

2

Check this line:

aa=new ArrayAdapter<String(getBaseContext(),android.R.layout.simple_list_item_1,l.get(0) );

Here use of l.get(0) is null as l is never initialized.

answered Aug 5, 2014 at 3:34

Illegal Argument

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2 Comments

JoeCoolman Over a year ago

ok, in the line before that I put l.get(0).add(""), I think "I added an empty string as first element in the l.get(0) string array" but again, now this line is causing java.lang null pointer exception.

Illegal Argument Over a year ago

@JoeCoolman l is null so any operation on l will result in nullpointer exception ArrayList<String> l = new ArrayList<String>(); this kind of initialization needs to be done first on most of the objects including arraylist

Aniruddha · Accepted Answer · 2014-08-05 05:26:05Z

0

Here l.get(0) is throwing NPE. You need to initialise ArrayList<ArrayList<String>> l like,

 ArrayList<ArrayList<String>> l = new ArrayList<ArrayList<String>>();

edited Aug 5, 2014 at 5:26

answered Aug 5, 2014 at 4:13

Aniruddha

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3 Comments

JoeCoolman Over a year ago

@Illegal Argument and you are both correct, I was reading more and I discovered how initialize one-dimension ArrayList using the double brace initialization method. Now, how it must be done for double-dimension ArrayList?

Aniruddha Over a year ago

Did you try my answer?? Try l = new ArrayList<ArrayList<String>>(); and let me know.

Aniruddha Over a year ago

@JoeCoolman Thanks for the accept :). You can up vote also. Happy coding :)

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