# Why i can't do operations for arrays to arrays of custom classes
**URL:** https://discourse.processing.org/t/why-i-cant-do-operations-for-arrays-to-arrays-of-custom-classes/44369
**Category:** Coding Questions
**Created:** [May 1, 2024, 6:58pm UTC](https://discourse.processing.org/t/why-i-cant-do-operations-for-arrays-to-arrays-of-custom-classes/44369 "2024-05-01T18:58:10Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@zlfp](https://discourse.processing.org/u/zlfp)
#### Post date: [May 1, 2024, 6:58pm UTC](https://discourse.processing.org/t/why-i-cant-do-operations-for-arrays-to-arrays-of-custom-classes/44369/1 "2024-05-01T18:58:10Z")
shorter, there is the code we need
```auto
class creature {
float xp,yp;
PImage ifa;
}
class animal extends creature {
animal(float sxp,float syp,PImage sifa) {
xp = sxp;
yp = syp;
ifa = sifa;
}
void NP(float nxp,float nyp) {
xp = nxp;
yp = nyp;
}
void nims(PImage nifa) {
ifa = nifa;
}
}
```
suppose we need a append an array of animals
```auto
animal[] a = new animal[0];
a = append(a, new animal(0,0, somePImage))
```
but, we have an error
```auto
Type mismatch: cannot convert from Object to somefile.animal[]
```
how to fix it?
p.s its processing 4.3 java
p.p.s don’t ask why I need this im creating games on processing
---
### Author:  [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [May 1, 2024, 7:26pm UTC](https://discourse.processing.org/t/why-i-cant-do-operations-for-arrays-to-arrays-of-custom-classes/44369/2 "2024-05-01T19:26:55Z")
- [Why use ArrayList instead of array with append()? - Processing 2.x and 3.x Forum](https://forum.Processing.org/two/discussion/8080/why-use-arraylist-instead-of-array-with-append.html)
---
### Author:  [@zlfp](https://discourse.processing.org/u/zlfp)
#### Post date: [May 1, 2024, 7:55pm UTC](https://discourse.processing.org/t/why-i-cant-do-operations-for-arrays-to-arrays-of-custom-classes/44369/3 "2024-05-01T19:55:56Z")
cause is not mine (its noting there in comment)
---
### Author:  [@Chrisir](https://discourse.processing.org/u/Chrisir)
#### Post date: [May 1, 2024, 8:43pm UTC](https://discourse.processing.org/t/why-i-cant-do-operations-for-arrays-to-arrays-of-custom-classes/44369/4 "2024-05-01T20:43:35Z")
Hello,
instead of
> [@zlfp](#):
>
> `a = append(a, new animal(0,0, somePImage))`
better
`a = (animal[]) append(a, new animal(0,0, somePImage))`
see: [append() / Reference / Processing.org](https://processing.org/reference/append_.html)
> When using an array of objects, the data returned from the function [append] must be cast to the object array’s data type.
> For example: _SomeClass[] items = (SomeClass[]) append(originalArray, element)_.
or in your case: `items = (SomeClass[]) append(originalArray, element)`
- with `(SomeClass[])` being the crucial part that tells (_casts_) the Object to be of kind `animal[]`
**Remark**
Instead of just “`a`” it might be wise to name it `listOfAnimals` or `arrAnimals` or so.
Chrisir
---
### Author:  [@zlfp](https://discourse.processing.org/u/zlfp)
#### Post date: [May 2, 2024, 10:10am UTC](https://discourse.processing.org/t/why-i-cant-do-operations-for-arrays-to-arrays-of-custom-classes/44369/5 "2024-05-02T10:10:56Z")
it works, thanx Chrisir 😁