calculates a value each frame?

What is the value float, String, object ...?

then im printing my arraylist.

I hope you are not doing this every frame that would slow it down.

I need to have a very big arralist with more than 800 000  values.

When you create the array list  define the initial capacity, this should help at runtime e.g.

1. // A million floats
2. ArrayList<Float> bigList = new ArrayList<Float>(1000000);

" I hope you are not doing this every frame that would slow it down."
Actually, it might be the cause of the crash, I recall users making the PDE to crash because they saturated the console...