Cannot push an Integer object into an generic array

Question

I'm trying to push Integer onto a generic array. Here's my code:

import java.lang.reflect.Array;

public class StackMain
{
    public void main (String[]args)
    {
        Integer[] oneStack = null;
        Integer a = new Integer("1");

        oneStack = (Integer[])Array.newInstance(Integer.class, 10);

        push(a, oneStack);
    }
}


public class Stack<T>
{
    private T[] oneStack;

    public void push(T item, T[] array)
    {
        array[1] = item; //dummy method for testing    
    }
}

But push(a, oneStack) gives me a "cannot find symbol" error for some reason. Should I use Integer[] instead of T[]? I thought that Integer was a generic ...

What does your Stack<T>.push intend to do? It isn't clear to me whether you want to push item to array or oneStack. — Haozhun
– Haozhun, Commented Jun 7, 2013 at 6:01
I would work on simplifying your code. I suspect it doesn't need to be doing half the things your code is doing. — Peter Lawrey
– Peter Lawrey, Commented Jun 7, 2013 at 6:17

Jon Skeet · Accepted Answer · 2013-06-07 06:09:46Z

5

push(a, oneStack); gives me cannot find symbol for some reason.

Yes, because you're trying to call it in StackMain, and it only exists in Stack<T>. You need to create a Stack<Integer> in order to call it:

Stack<Integer> stack = new Stack<Integer>();
stack.push(a, oneStack);

If you want to allow it to be called without creating an instance, it needs to be a static method. (I'm assuming that in reality, there's more code.)

(If you're very new to Java, I'd suggest concentrating on the really core stuff such as invoking methods and creating objects before you worry about generics. You'll need to tackle them soon, but if you try to learn about them while you're still getting to grips with the very basics, it'll slow you down in the long run.)

edited Jun 7, 2013 at 6:09

answered Jun 7, 2013 at 5:58

Jon Skeet

1.5m893 gold badges9.3k silver badges9.3k bronze badges

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

3 Comments

david Over a year ago

does stack refer to a stack object or it's just used to access the method in the stack class?

david Over a year ago

ah thanks it's working, it seems that i needed to instantiate a stack object even though i didn't have any constructor.

Jon Skeet Over a year ago

@david: You do have a constructor: the default public parameterless constructor that the compiler provides for you if you don't specify any constructors explicitly.

Simon Curd · Accepted Answer · 2013-06-07 05:59:55Z

0

You need to create an instance of your stack object before calling the push(...) method on it

answered Jun 7, 2013 at 5:59

Simon Curd

8606 silver badges12 bronze badges

Comments

Harish Kumar · Accepted Answer · 2013-06-07 06:05:48Z

0

The method push is not visible to StackMain class (as it is in Stack class) unless you create an instance of Stack and then refer it. Either you should localize this method to StackMain class or create an instance of Stack class.

answered Jun 7, 2013 at 6:05

Harish Kumar

5282 silver badges15 bronze badges

Collectives™ on Stack Overflow

Cannot push an Integer object into an generic array

3 Answers 3

3 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

3 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related