Java Array Result = null

Question

I have problem with my double arrays. After i run my File i got "null" values.

I do not know to parse this array above.

public class TestDesposit {
    public static void main(String[] args) {
        double [] rev = {1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 12.0};
        double [] exp = {0.0, 1.0, 0.0, 0.0, 0.0, 0.0, 0.0, 3.0, 0.0, 0.0, 0.0, 0.0};

        Result res = new Result (exp, rev);
        System.out.println(Arrays.toString(res.Resultat()));
    }
}

public class Result {
    double [] mExpenses;
    double [] mRevenue;
    double [] mResult;

    public Result (double[] pExpenses, double[] pRevenue) {
        mExpenses = pExpenses;
        mRevenue = pRevenue; 
    }

    public double [] Resultat () {
        for (int i = 0; i == 12; i++) {
            mResult[i] = mRevenue[i] - mExpenses[i];
        }
        return mResult;
    }   
}

Where do you ever initialize the mResult array? It's null until you assign it a viable array. — Hovercraft Full Of Eels, Oct 12 '16 at 09:18
And your loop condition is broken: `i == 12` should be `i < 12` or better, `i < mRevenue.length` — Jon Skeet, Oct 12 '16 at 09:19
You also are using `i == 12` when it should be something like `i <= 12` — Benjamin Lowry, Oct 12 '16 at 09:19
This isn't a NullPointerException problem - no exception is thrown by the given code, because it never gets into the body of the loop. There are two bugs here: non-initialization of `mResult`, and the loop condition. — Jon Skeet, Oct 12 '16 at 09:20
Some parentheses are also missing at the end of the class `TestDesposit `? — ujulu, Oct 12 '16 at 09:26
And hint: your code is **super** confusing. Having a **field** mResult that some (badly named) method Resultat returns ... that is just plain **ugly**. Dont do that. If you provide access to a field, call the method "getSomething()"; but if you want the method to really compute something than have it create/return a local variable instead. — GhostCat, Oct 12 '16 at 09:30

Benjamin Lowry · Accepted Answer · 2016-10-12T09:34:04.910

You need to initialize your mResult array. Of course, this creates problems if your input arrays are not always going to have a length of 12, but that's a different problem.

You can try something like this:

double[] mResult = new double[12];

Then, as also people have been pointing out, you should change your for loop in Resultat to something like this:

for (int i = 0 ; i < mRevenue.length ; i++){

Note, that you can also use mResult.length and mExpenses.length as they will also be the same in your scenario.

score 0 · Answer 2 · answered Oct 12 '16 at 09:29

At first, mResult is not init, so it is null object Second, this code

for (int i=0 ; i ==12; i++){.. }

never run , i think u should change like that

public double [] Resultat (){
   mResult  = new double[12];
        for (int i=0 ; i <12; i++){
        mResult[i] = mRevenue[i] - mExpenses[i];
        }
    return mResult;
    }

score -1 · Answer 3 · answered Oct 12 '16 at 09:19

-1

for (int i=0 ; i ==12; i++){

is wrong. You should try i<12

answered Oct 12 '16 at 09:19

tomas

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Java Array Result = null

3 Answers3