Why I can't add an Object to an Object[] array?

Question

I know I can use ArrayList for this, but I don't understand why I can't add an Object intance to the following Object[] array?

class Penguin {
    public void say(){
        System.out.println("Hi, I am a penguin!");
    }
}
public class TempTest {
    private Object[] items;
    private int next = 0;
    private int i = 0;
    public void add(Object x){
        if(next < items.length)
            items[next++] = x;
    }
    public boolean end() { return i == items.length; }
    public Object current() { return items[i]; }
    public void next() { if(i < items.length) i++; }

    public static void main(String[] args) {
        Object[] obj = new Object[5];
        Object p = new Penguin();
        obj.add(p);
    }
}

Eclipse screenshot

Why do you think an array (in Java) has an add method? Read some tutorials, please. The Arrays chapter in the Java Tutorials tells you more. — Seelenvirtuose
– Seelenvirtuose, Commented Mar 31, 2014 at 7:28
Indeed, I was too quick. Though I added add method it belongs to TempTest not Object[]. My bad. — tastyminerals
– tastyminerals, Commented Mar 31, 2014 at 7:30

Rogue · Accepted Answer · 2014-03-31 07:25:37Z

3

Arrays don't have an add function, you're thinking of Collections.

When you have an array of a specific size, you can set the indexes of that array:

Object[] arr = new Object[2];
arr[0] = /* your object */;

//...
Object yourObj = arr[0]; //returns that object

As pointed out by @SubhrajyotiMajumder , try calling your class' local implementation of the method:

this.add(yourObj);

And from there potentially refactor code so that you are editing the same array each time, not one that you made locally.

answered Mar 31, 2014 at 7:25

Rogue

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4 Comments

sandymatt Over a year ago

Arrays aren't data structures? I think you meant Collection.

Rogue Over a year ago

@KepaniHaole Correct, slight slip on my part!

tastyminerals Over a year ago

I wish I could access Penguin object with arr[0].say();

Rogue Over a year ago

Don't make it an Object array, make it an array of some common interface that has the say() method :)

Maroun · Accepted Answer · 2014-03-31 07:25:39Z

3

Because obj is an array, you simply add elements by indexes:

obj[0] = someObject;

In your case, you should add elements using a loop, from 0 to 4.

See Arrays for more information.

answered Mar 31, 2014 at 7:25

Maroun

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Comments

Juned Ahsan · Accepted Answer · 2014-03-31 07:25:35Z

2

Object class does not have any method called add. Its an array so u need to put objects using index.

Also creating an array of Object is not a good idea unless u really have a real need of doing so. Better use collections.

answered Mar 31, 2014 at 7:25

Juned Ahsan

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Comments

newuser · Accepted Answer · 2014-03-31 07:26:16Z

1

Assign value for an array

obj[0] = p;

instead of

obj.add(p);

answered Mar 31, 2014 at 7:26

newuser

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Rakesh KR · Accepted Answer · 2014-03-31 07:28:31Z

1

obj is an array, you can add elements by

obj[0] = object1;

answered Mar 31, 2014 at 7:28

Rakesh KR

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ARUN · Accepted Answer · 2014-03-31 07:29:23Z

0

You need to mention object array index there instead of add method .

obj [array index] = p ;

answered Mar 31, 2014 at 7:29

ARUN

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