# Unable to append to an array of G4P objects
**URL:** https://discourse.processing.org/t/unable-to-append-to-an-array-of-g4p-objects/19898
**Category:** Libraries
**Created:** [April 18, 2020, 6:30pm UTC](https://discourse.processing.org/t/unable-to-append-to-an-array-of-g4p-objects/19898 "2020-04-18T18:30:47Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@David](https://discourse.processing.org/u/David)
#### Post date: [April 18, 2020, 6:30pm UTC](https://discourse.processing.org/t/unable-to-append-to-an-array-of-g4p-objects/19898/1 "2020-04-18T18:30:47Z")
I can create arrays of G4P objects and access them using an index or subscript, but I don’t seem to be able to append to an array of G4P objects. I get an error message “cannot convert from Object to GPanel[]” on the line with “append()”. This works for arrays of other types of object such as Strings. Is there something special about G4P objects? I do have a reason for wanting to do this, although it’s not obvious from this stripped-down example.
Here’s my source code:
```auto
import g4p_controls.*;
public void setup() {
size(800,600,JAVA2D);
String[] sa = {};
sa = append(sa, "MA");
println(sa.length);
for (int i=0; i < sa.length; i++) println(sa[i]);
GPanel[] panels = {};
GPanel panel = new GPanel(this,0,0,200,200);
panels = append(panels,panel);
println(panels.length);
}
public void draw() {
}
```
Thanks.
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [April 18, 2020, 7:10pm UTC](https://discourse.processing.org/t/unable-to-append-to-an-array-of-g4p-objects/19898/2 "2020-04-18T19:10:17Z")
[Processing.org/reference/append\_.html](http://Processing.org/reference/append_.html)
---
### Author:  [@David](https://discourse.processing.org/u/David)
#### Post date: [April 18, 2020, 7:13pm UTC](https://discourse.processing.org/t/unable-to-append-to-an-array-of-g4p-objects/19898/3 "2020-04-18T19:13:39Z")
Yes, that’s where I got the String example (append(sa1, “MA”)) from. My question is, why does it work for String objects but not GPanel objects?
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [April 18, 2020, 7:16pm UTC](https://discourse.processing.org/t/unable-to-append-to-an-array-of-g4p-objects/19898/4 "2020-04-18T19:16:11Z")
> [@David](#):
>
> , why does it work for String objects but not GPanel objects?
It’s already been explained there:
> When using an array of objects, the data returned from the function must be cast to the object array’s data type.
---
### Author:  [@David](https://discourse.processing.org/u/David)
#### Post date: [April 18, 2020, 7:25pm UTC](https://discourse.processing.org/t/unable-to-append-to-an-array-of-g4p-objects/19898/5 "2020-04-18T19:25:24Z")
But they’re the same, aren’t they? I have an array of GPanel’s, and the constructor returns a GPanel.
If this is what you mean, it doesn’t work either (same error message):
` panels = append(panels,(GPanel)panel);`
---
### Author:  [@David](https://discourse.processing.org/u/David)
#### Post date: [April 18, 2020, 7:45pm UTC](https://discourse.processing.org/t/unable-to-append-to-an-array-of-g4p-objects/19898/6 "2020-04-18T19:45:10Z")
Now I understand. I changed line to the following, and it’s working now.
` panels = (GPanel[]) append(panels,panel);`
Thanks.
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [April 18, 2020, 7:50pm UTC](https://discourse.processing.org/t/unable-to-append-to-an-array-of-g4p-objects/19898/7 "2020-04-18T19:50:05Z")
Using `(cast)` is indeed not ideal. If you wish, you can override **append()** pasting the 3 methods below on your sketch, so `(cast)` isn’t needed anymore: 😉
```java
static final T[] expand(final T[] list) {
return expand(list, list.length << 1);
}
static final T[] expand(final T[] list, final int newSize) {
return java.util.Arrays.copyOf(list, newSize);
}
static final T[] append(final T[] list, final T value) {
final T[] arr = expand(list, list.length + 1);
arr[arr.length - 1] = value;
return arr;
}
```
>
>