null pointer exception error calling method

Question

I get this null pointer exception error if i call a method. if (farm1.cropStat(row, col) )

here's the method

public boolean cropStat(int row, int col)
{
    if( !( field1[row][col].harvested ) && field1[row][col] != null  )       
    {
        return true;
    }
    else
    {
        return false;
    }
}

here's the initialization

public void initializeCrops()
{
    Random rnd = new Random();
    int rRow=-1, cCol=-1;
    int i, j;

    for (i = 0; i< 74; i++)
    {   
        while(rRow <0 || cCol <0)
        {
            rRow = rnd.nextInt() % 104;
            cCol = rnd.nextInt() % 104;
        }
        field1[rRow][cCol] = new Crops(rRow, cCol);
    }  
 }

pls help :(

Sergey Kalinichenko · Accepted Answer · 2015-03-01 11:49:46Z

1

Whenever you see a pattern that looks like this

if (someCondition) {
    return true;
} else {
    return false;
}

replace it with the equivalent

return someCondition.

It is the same thing.

As far as the error goes, you need to reverse the order of your checks in order to see that the item is not null before referencing it:

return field1[row][col] != null && !( field1[row][col].harvested );

Operator && is designed in such a way that once it sees that the result is going to be false, it stops further evaluation. In the example above, && will stop if field1[row][col] is null, preventing null pointer exception.

answered Mar 1, 2015 at 11:49

Sergey Kalinichenko

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2 Comments

user4620058 Over a year ago

I followed your suggestion but I still get the null pointer exception problem. @dasblinkenlight

Sergey Kalinichenko Over a year ago

@JedrekFadul A more conservative check would go like this: field1!=null && field1[row] != null && field1[row][col] != null && !( field1[row][col].harvested ). Usually, though, this indicates that the setup hasn't set the array up in a way to make all cells of 2D array available.

shimonb89 · Accepted Answer · 2015-03-01 11:48:28Z

0

You did not initialize field1 anywhere, so it is null when you try to assign values into it.

answered Mar 1, 2015 at 11:48

shimonb89

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1 Comment

user4620058 Over a year ago

I did: @shimonb89 public Farm() { field1 = new Crops[104][104]; }

René Winkler · Accepted Answer · 2015-03-01 11:51:50Z

0

Reverse the order of the expressions in the if statement:

if( field1[row][col] != null && !( field1[row][col].harvested ))

answered Mar 1, 2015 at 11:51

René Winkler

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