NullPointerException in array

Question

I keep getting a NullPointerException at (see below). Everything works fine in C#, but in android it breaks?

arrDBNumbers is full and code is supposed to run through and count the amount of #1, #2, #3 and so on to #49 adding 1 to arrFreq[i][1] to fill arrFreq with the total count of the numbers.

It runs through the if statement till k hits 6 where arrDBNumbers[0][6] is 1, then jumps inside if statement and then breaks? I'm not sure whats going on here any advice thanks in advance T

Integer[][] arrDBNumbers = new Integer[100][8];
Integer[][] arrFreq = new Integer[49][2];


for (int i = 0; i < 49; i++){
    for (int j = 0; j < 49; j++){
        for (int k = 1; k < 7; k++){
            if (arrDBNumbers[j][k] == (i + 1)){
                arrFreq[i][1]++;     //  < here is where I get Exception?
            }
        }
    }
}

While the question's been answered.. I think that's also susceptible to an IOBE.. k > 2.. also i+1 if i is 48..? — Lews Therin
– Lews Therin, Commented May 1, 2013 at 17:23
It is a java question not android. It is better to change the title — Afshin Moazami
– Afshin Moazami, Commented May 1, 2013 at 17:24

AllTooSir · Accepted Answer · 2013-05-01 17:29:11Z

5

Because just writing

Integer[][] arrFreq = new Integer[49][2];

means you have initialized the array with all null elements because it is an array of Integer Objects and Object's default value will be null reference. Hence,

arrFreq[i][1]++;  // trying null++;

gives NullPointerException.

This wouldn't have been the case if you had used an array of primitives, which will default to an array of 0s.

int[][] arrFreq = new int[49][2];

edited May 1, 2013 at 17:29

answered May 1, 2013 at 17:22

AllTooSir

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2 Comments

the homeless coder Over a year ago

Hi thanks for quick reply, so Integer[][] arrFreq; and leave it at that yea.

AllTooSir Over a year ago

not sure why that is but it works : Please check Java tutorials to know what are the default values of primitives and references.

Vegard · Accepted Answer · 2013-05-01 17:24:42Z

0

Integer is a container for int, in your case you have lots of null objects. if you use int instead it will work as you expect.

answered May 1, 2013 at 17:24

Vegard

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