Why app crashing? NullPointerException when assigning Arraylist to Array

Question

Exhibit[] listOfEx = exhibits.toArray(new Exhibit[exhibits.size()]);;
        String[] listOfSt = null;

        for (int i = 0; i < exhibits.size(); i++){
            Log.d("DEBUG", String.valueOf(exhibits.size()));
            listOfSt[i] = listOfEx[i].getName();
            Log.d("DEBUG", listOfSt[i]);
        }

        ListView list = (ListView) findViewById(android.R.id.list);
                list.setAdapter(new ArrayAdapter<String>(this, 
                        R.layout.listview_item, listOfSt));

My app crashes where it assigns in loop. I get this:

07-18 22:43:32.760: E/AndroidRuntime(28545): java.lang.RuntimeException: Unable to start activity ComponentInfo{edu.foothill.junk/edu.foothill.junk.MainActivity}: java.lang.NullPointerException

Please let me know if more info needed. Thank you in advance.

Point out which line the exception occured on.

Gabe Sechan
– Gabe Sechan

2014-07-19 05:50:33 +00:00
Commented Jul 19, 2014 at 5:50 — Gabe Sechan
– Gabe Sechan, Commented Jul 19, 2014 at 5:50

Alexandre Santos · Accepted Answer · 2014-07-19 05:51:28Z

2

What do you expect this code to do?

String[] listOfSt = null;

It creates a null variable, right?

And then you use the null variable (without having initialized it first):

 listOfSt[i] = listOfEx[i].getName();

answered Jul 19, 2014 at 5:51

Alexandre Santos

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Christian Tapia · Accepted Answer · 2014-07-19 05:51:37Z

0

You have to initialize the array listOfSt with an empty array, not null:

String[] listOfSt = new String[length];

where length will be the length of the array, so it will depend on how many items you want it to store. If you want it to have the same length than listOfEx, you can use

String[] listOfSt = new String[listOfEx.length];

answered Jul 19, 2014 at 5:51

Christian Tapia

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