Array error java.lang.ArrayIndexOutOfBoundsException

Question

I'm very new to Java, currently learning arrays. So I was making this little program to input gas used and miles traveled to calculate miles per gallon, but whenever I run the program I get an error at line 21 (miles[counter] = input.nextInt();) the error says:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
at GasMileage.inputGasAndMiles(GasMileage.java:21)
at GasMileage.main(GasMileage.java:44)

I have no idea what this means nor do I know how to fix it, It'd be great if I could get some help on this.

int counter = 0;
int[] gallons, miles = new int[trips];

public void inputGasAndMiles(){

    for(counter = 0; counter <= trips; counter++){
        System.out.print("\nInput miles traveled: ");
        miles[counter] = input.nextInt();

        System.out.print("Input gallons of fuel used: ");
        gallons[counter] = input.nextInt();
    }
}

EDIT

public void askTrips(){
    System.out.print("How many trips would you like to calculate for: ");
    trips = input.nextInt();
}

Stack trace:

public static void main(String[]args){
    GasMileage gas = new GasMileage();

    gas.askTrips();
    gas.inputGasAndMiles();
    gas.calculate();
    gas.display();
}

@Legend the initial value is set by the user, I forgot to show the code above. — Wot Wat
– Wot Wat, Commented Mar 27, 2013 at 18:01

Ankit · Accepted Answer · 2013-03-27 18:04:31Z

3

it should be for (counter = 0; counter < trips; counter++)

because, array index starts from zero, so max index would be (size-1) not size

EDIT:

int trips= 0; //any +ve value
int[] gallons =  new int[trips], miles = new int[trips];

public void inputGasAndMiles(){

for(counter = 0; counter < trips; counter++){
    System.out.print("\nInput miles traveled: ");
    miles[counter] = input.nextInt();

    System.out.print("Input gallons of fuel used: ");
    gallons[counter] = input.nextInt();
}

}

edited Mar 27, 2013 at 18:04

answered Mar 27, 2013 at 17:56

Ankit

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8 Comments

user1181445 Over a year ago

This does not provide the same error. trips is most likely 0, resulting in the index out of range at index 0.

Ankit Over a year ago

still it wont go out of index

user1181445 Over a year ago

It does not answer his question. An array of size 0 does not have an element at index 0.

user1181445 Over a year ago

@WotWat, make sure trips is designated initially above 0.

Ankit Over a year ago

@Legend then how will it pass the case 0<0 ? (where 1st 0 is start index, and 2nd is size)

|

user2030471 · Accepted Answer · 2013-03-27 17:56:29Z

0

Change this

counter <= trips

to this

counter < trips

in the for construct there.

answered Mar 27, 2013 at 17:56

user2030471

Comments

Addict · Accepted Answer · 2013-03-27 17:58:07Z

0

Change

for(counter = 0; counter <= trips; counter++)

to

for(counter = 0; counter < trips; counter++)

index of array start from 0 to (length -1 )

answered Mar 27, 2013 at 17:58

Addict

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Comments

Miguel Rodrigues · Accepted Answer · 2013-03-27 18:06:07Z

0

Try this

int counter = 0;
int[] gallons, miles = new int[trips];

public void inputGasAndMiles() {
    for(counter = 0; counter < trips; counter++) {
        System.out.print("\nInput miles traveled: ");
        miles[counter] = input.nextInt();

        System.out.print("Input gallons of fuel used: ");
        gallons[counter] = input.nextInt();
    }   
}

edited Mar 27, 2013 at 18:06

Miguel Rodrigues

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answered Mar 27, 2013 at 17:57

Jabir

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Comments

Vishal K · Accepted Answer · 2013-03-27 18:13:07Z

0

for(counter = 0; counter <= trips; counter++)

change it to :

for(counter = 0; counter < trips; counter++)

The size of your gallons array is trips .Since the first Index starts with 0 so the last index of your gallons array will be trips-1. And in your code you are trying to access the element at index trips when (counter == trips) in for loop becomes true, this leading to ArrayIndexOutOfBounException

edited Mar 27, 2013 at 18:13

answered Mar 27, 2013 at 17:56

Vishal K

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1 Comment

jsedano Over a year ago

Yes, remember, arrays start at 0 not 1, so if you want to iterate over an array of 10 elements, you need to go from 0 to 9

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