Java: Can't add an int to an arraylist

Question

I've created an empty arraylist here:

private ArrayList<OrderItem>  conveyorBelt = new ArrayList<OrderItem>(10);

And in the same class, I've created a method where I add item into the conveyorBelt by inputting the orderNum (which is an int). This is what the method looks like:

public void addToConveyorBelt( int orderNum )
{
OrderItem oi;
conveyorBelt.add(oi.getOrderNum(orderNum)); // line 4
}

This doesn't work. I get a compile error on line 4, saying this: http://i52.tinypic.com/ny8n86.jpg

Anyone know where i'm going wrong with this?

p.s. - the OrderItem contains one variable called theOrderNum and a method that calls it called getOrderNum.

why do you need to get the order num from the orderitem if you already have the order num? Surely what you are trying to do is create a new OrderItem from an order num and add that to the list? — Robert
– Robert, Commented Dec 25, 2010 at 1:25
Yes, that's what i'm trying to do. I apologise for not making myself clear. — hteeT
– hteeT, Commented Dec 25, 2010 at 1:57

Brett Kail · Accepted Answer · 2010-12-25 04:13:09Z

3

According to the error message, the method signature of "getOrderNo" does not accept a parameter of type "int". From what you've given, I suspect the OrderItem class looks something like this:

public class OrderItem {
    private int theOrderNum;

    OrderItem(int num) {
        theOrderNum = num;
    }

    public int getOrderNum() {
        return theOrderNum;
    }
}

If so, you want to create a new OrderItem from the orderNum parameter, and then add it to conveyerBelt:

public void addToConveyorBelt(int orderNum) {
    OrderItem oi = new OrderItem(orderNum);
    conveyorBelt.add(oi);
}

If not, you need to update the question to include more information about the OrderItem class.

answered Dec 25, 2010 at 4:13

Brett Kail

34k2 gold badges88 silver badges93 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Falmarri · Accepted Answer · 2010-12-25 01:21:37Z

1

getOrderNum obviously returns an int. Your arraylist is an arraylist of OrderItems. What are you expecting to happen?

Not only that, but you're guarunteed a null pointer exception there because oi isn't initialised.

answered Dec 25, 2010 at 1:21

Falmarri

48.7k43 gold badges158 silver badges196 bronze badges

2 Comments

Reboot Over a year ago

Not entirely correct. Local variables in a method are not initialized to null if they are not assigned. Like this the compiler will complain that the variable is not initialized.

hteeT Over a year ago

Thanks for the clear up Reboot. I was going to reply with something along those lines. Thanks anyways Falmarri.

Robert · Accepted Answer · 2010-12-25 01:28:50Z

1

I suspect your method should be something like this:

public void addToConveyorBelt(int orderNum){
    OrderItem oi = getOrderItem(orderNum);
    conveyorBelt.add(oi); 
}

answered Dec 25, 2010 at 1:28

Robert

8,64910 gold badges42 silver badges57 bronze badges

1 Comment

hteeT Over a year ago

Thanks Robert. But on line three I get a compile error saying "cannot find symbol - method getOrderNum(orderNum)". (even though you said "getOrderItem", I put "getOrderNum" because that's what the method is called in OrderItem). Know what might be the problem?

user467871 · Accepted Answer · 2010-12-25 04:58:11Z

0

you define arraylist like that

private ArrayList<OrderItem>  conveyorBelt = new ArrayList<OrderItem>(10);

It means you can only add OrderItem to the list

public void addToConveyorBelt( int orderNum )
{
OrderItem oi;
conveyorBelt.add(oi.getOrderNum(orderNum)); // here it fails
}

Change it as follows

public void addToConveyorBelt( int orderNum )
    {
    OrderItem oi = new OrderItem(orderNum);
    conveyorBelt.add(oi); // here it fails
    }

oi.getOrderNum(orderNum) should throw NullPointerException

answered Dec 25, 2010 at 4:58

user467871

1 Comment

hteeT Over a year ago

Thanks hilal. This is also useful (NullPointerException part).

Collectives™ on Stack Overflow

Java: Can't add an int to an arraylist

4 Answers 4

Comments

2 Comments

1 Comment

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

2 Comments

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related