NullPointerException in integer array

Question

I am having a problem with a null pointer exception. Please specify some general cases of it.

Here is my code:

public class GuessActivity extends ListActivity implements OnClickListener
{
EditText GNum;
Button nxt;
int[] a = new int[4];
int[] d = new int[4];
int t = 0;
ArrayList<HashMap<String, String>> output = new ArrayList<HashMap<String, String>>();
HashMap<String, String> out = new HashMap<String, String>();
String KEY_NUM , KEY_BULLS , KEY_COWS;


protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.guess_activity);

    GNum = (EditText) findViewById(R.id.etGuessNum);
    nxt = (Button) findViewById(R.id.btNxt);
    a = getIntent().getExtras().getIntArray("num");

    nxt.setOnClickListener(this);
}


@Override
public void onClick(View v) 
{
    if(v.getId() == R.id.btNxt)
    {
        String gN = GNum.getText().toString();
        int l = gN.length();
        int b =0;
        int c =0;
        if(l!=4)
        {
            Toast.makeText(getApplicationContext(),"Number should be of 4 digits",
                    Toast.LENGTH_LONG).show();
        }
        else
        {
            t++;
            int x = Integer.parseInt(gN);

            for(int i=0;i<4;i++)
            {
                d[i] = x%10;
                x = x/10;
            }
            if(t>8)
                Toast.makeText(getApplicationContext(), "You Lost the Game",
                        Toast.LENGTH_SHORT).show();
            else
            {

                if(d[0] == a[0])
                    b++;
                if(d[0] == a[1] || d[0] == a[2] || d[0] == a[3])
                    c++;
                if(d[1] == a[1])
                    b++;
                if(d[1] == a[0] || d[1] == a[2] || d[1] == a[3])
                    c++;
                if(d[2] == a[2])
                    b++;
                if(d[2] == a[1] || d[2] == a[0] || d[2] == a[3])
                    c++;
                if(d[3] == a[3])
                    b++;
                if(d[3] == a[1] || d[3] == a[2] || d[3] == a[0])
                    c++;

                if(b == 4)
                    Toast.makeText(getApplicationContext(), "You Win",
                        Toast.LENGTH_SHORT).show();
            }
            out.put(KEY_NUM , gN);
            out.put(KEY_BULLS ,String.valueOf(b));
            out.put(KEY_COWS , String.valueOf(c));

            output.add(out);


            ListAdapter adapter = new SimpleAdapter(this, output,
                    R.layout.list_item,
                    new String[] { KEY_NUM , KEY_BULLS , KEY_COWS}, new int[] {
                            R.id.tvGuessNum , R.id.tvBulls ,R.id.tvCows });

            setListAdapter(adapter);
            ListView lv = getListView();
        }
    }
}
}

Here is the stack trace:

03-04 06:32:58.960: W/dalvikvm(844): threadid=1: thread exiting with uncaught exception (group=0xb3ab2ba8)
03-04 06:32:58.970: E/AndroidRuntime(844): FATAL EXCEPTION: main
03-04 06:32:58.970: E/AndroidRuntime(844): Process: com.example.game, PID: 844
03-04 06:32:58.970: E/AndroidRuntime(844): java.lang.NullPointerException
03-04 06:32:58.970: E/AndroidRuntime(844):  at com.example.game.GuessActivity.onClick(GuessActivity.java:66)
03-04 06:32:58.970: E/AndroidRuntime(844):  at android.view.View.performClick(View.java:4438)
03-04 06:32:58.970: E/AndroidRuntime(844):  at android.view.View$PerformClick.run(View.java:18422)
03-04 06:32:58.970: E/AndroidRuntime(844):  at android.os.Handler.handleCallback(Handler.java:733)
03-04 06:32:58.970: E/AndroidRuntime(844):  at android.os.Handler.dispatchMessage(Handler.java:95)
03-04 06:32:58.970: E/AndroidRuntime(844):  at android.os.Looper.loop(Looper.java:136)
03-04 06:32:58.970: E/AndroidRuntime(844):  at android.app.ActivityThread.main(ActivityThread.java:5017)
03-04 06:32:58.970: E/AndroidRuntime(844):  at java.lang.reflect.Method.invokeNative(Native Method)
03-04 06:32:58.970: E/AndroidRuntime(844):  at java.lang.reflect.Method.invoke(Method.java:515)
03-04 06:32:58.970: E/AndroidRuntime(844):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
03-04 06:32:58.970: E/AndroidRuntime(844):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
03-04 06:32:58.970: E/AndroidRuntime(844):  at dalvik.system.NativeStart.main(Native Method)

Line 66 is in the onClick method: d[i] = x % 10

Have you checked which value is null at the line of your where your exception is thrown? — Smutje
– Smutje, Commented Mar 4, 2014 at 11:56
general cases. A null pointer exception happens when you try to use ("dereference") an object variable which has had no object assigned to it (it is "uninitialised"). All objects variables in Java are set to null until you do initialise them. Object myObject; myObject.toString(); gives NullPointerException. Object myObject = new Object();myObject.toString(); works fine. BTW, learn to use the debugger, then finding these is really easy. — Simon
– Simon, Commented Mar 4, 2014 at 11:58
Also, don't be lazy. Use proper names, with proper naming conventions, for your code. You will not be able to debug your own code in 6 months because it is so hard to read. — Simon
– Simon, Commented Mar 4, 2014 at 12:01

Ben Pearson · Accepted Answer · 2014-03-04 11:59:32Z

2

Looks like the EditText (R.id.etGuessNum) doesn't have a value in it.

You should sanitize your input to avoid null references. I would also advise you check to see the value that they have entered is a valid number.

I would also have a quick read through naming conventions for Java.

answered Mar 4, 2014 at 11:59

Ben Pearson

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4 Comments

Ross Drew Over a year ago

wouldn't this throw a NumberFormatException instead of a NullPointerException?

Manuel Allenspach Over a year ago

Also, he checks for the length of the EditText. It would print a toast.

Ben Pearson Over a year ago

@Manu - if the length isn't 4, it would step in to the else block.

Ben Pearson Over a year ago

@RossDrew You're right. It must have been on another line.

Manuel Allenspach · Accepted Answer · 2014-03-04 12:02:03Z

0

Your 3 Strings KEY_NUM, KEY_BULLS, KEY_COWS are null.
Also, are you sure a is not null? a = getIntent().getExtras().getIntArray("num"); might return null.

Change

if(l!=4)
{
    Toast.makeText(getApplicationContext(),"Number should be of 4 digits",
            Toast.LENGTH_LONG).show();
}

to

if(l!=4)
{
    Toast.makeText(getApplicationContext(),"Number should be of 4 digits",
            Toast.LENGTH_LONG).show(); 
    return;
}

answered Mar 4, 2014 at 12:02

Manuel Allenspach

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4 Comments

Ross Drew Over a year ago

the NPE is before that.

Ross Drew Over a year ago

Isn't the problem on line d[i] = x%10;

Manuel Allenspach Over a year ago

It can't be, because d, i and x are ints (or arrays of int), which don't throw a NPE

Ross Drew Over a year ago

That's what he says in the description.

Unii · Accepted Answer · 2014-03-04 11:59:03Z

-1

change this:

String gN = GNum.getText().toString(); //can be null

to:

String gN = GNum.getText().toString(); //can be null
if(gN == null) 
return;

int l = gN.length(); //if edit text is empty this will be null

answered Mar 4, 2014 at 11:59

Unii

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2 Comments

Blackbelt Over a year ago

getText never returns null. Check the documentation

Ross Drew Over a year ago

and Integer.parseInt(null) would throw a different exception to the one shown in this case

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