Java For-Loop for only items in arrays

Question

I'm not sure if I'm wording this correctly. I have an array policies[10], it can hold 10 floats.

I have a method that adds a float to the array when it's initialized. I have another method that totals up all the floats in the array together. The thing is that when I only have 3/10 of the array filled up, I get a null error. Can someone show me how I can fix this?

policies is a list of a class, Policy.

public float totalCoverage(){
    float total = 0;
    for (Policy x : policies){
        total += x.amount;
                }
    return total;
}

For my test, I have 3/10 arrays, if i change the array size from 10 to 3, it works.

consider using getter and setter methods instead of directly accessing members like x.amount — Nandkumar Tekale
– Nandkumar Tekale, Commented Feb 5, 2013 at 11:53

Jon Skeet · Accepted Answer · 2013-02-05 11:50:38Z

5

Well presumably you've got some elements of your array which have null values. You can just do:

for (Policy x : policies) {
    if (x != null) {
        total += x.amount;
    }
}

A better change would be to use a dynamically-sized collection like ArrayList, so that you didn't have null values to consider in the first place.

answered Feb 5, 2013 at 11:50

Jon Skeet

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1 Comment

user1692517 Over a year ago

yup! that's it! so simple, i can't believe I let that slip out. Thank you very much

mericano1 · Accepted Answer · 2013-02-05 11:51:02Z

0

Did you try

public float totalCoverage(){
    float total = 0;
    for (Policy x : policies){
        if (x != null)
        total += x.amount;
                }
    return total;
}

answered Feb 5, 2013 at 11:51

mericano1

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Comments

PermGenError · Accepted Answer · 2013-02-05 11:51:18Z

0

For my test, I have 3/10 arrays, if i change the array size from 10 to 3, it works.

If i can interpret correctly, you only have 3 elements initialized in your array, remaining 7 elements are not initializaed, initializing the array doesn't mean that array elements are initialized. thus they get their default value. i..e, null thus when you call null.amount it throw NPE.

Null check :

for (Policy x : policies) {
    if (x != null) {
        total += x.amount;
    }
    else {
         System.out.println("x is null");
     }
}

answered Feb 5, 2013 at 11:51

PermGenError

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Comments

Narendra Pathai · Accepted Answer · 2013-02-05 12:03:29Z

0

public float totalCoverage(){

    float total = 0;
    for (int i = 0; i < array.length;i++){
       if(array[i] != null)
          total = total + array[i]
                }
       return total;
}

edited Feb 5, 2013 at 12:03

Narendra Pathai

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answered Feb 5, 2013 at 11:53

M.Kreusburg

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2 Comments

Jon Skeet Over a year ago

Why would you suggest using an explicit indexed for loop instead of the enhanced for loop?

Narendra Pathai Over a year ago

@JonSkeet one possibility can be non creation of iterator objects that are used in enhanced for loops. We work in performance critical environments and found in profiling that there were huge no of iterator objects created. So we explicitly used indexed loop.

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