Java – Clearing the global ArrayList also clears the other

I have a very strange bug.

I’m writing a generic class and in one of its methods, there’s a weird thing. Here is the class code (incomplete):

public abstract class GenericFragment<M extends BaseModel, A extends BaseAdapter> extends HtmlFragment {

private ArrayList<M> datas = new ArrayList<>();    
    private A adapter;

protected abstract String getUrl();

protected abstract A setAdapter();

protected A getAdapter() {

if(adapter == null) {
             adapter = setAdapter();
        }

return adapter;
    }

protected ArrayList<M> getDatas() {
        return datas;
    }

protected void refreshData(ArrayList<M> datas) {

Log.d("before glob", String.valueOf(this.datas.size()));
        Log.d("before loc", String.valueOf(datas.size()));

this.datas.clear();

Log.d("clear glob", String.valueOf(this.datas.size()));
        Log.d("clear loc", String.valueOf(datas.size()));

this.datas.addAll(datas);

Log.d("after glob", String.valueOf(this.datas.size()));
        Log.d("after loc", String.valueOf(datas.size()));

getAdapter().notifyDataSetChanged();
    }
}

When I call the function refreshData(), the global ArrayList is cleared and the local ArrayList is cleared. Here is the log:

D/niviel: before glob: 5
D/niviel: before loc: 5
D/niviel: clear glob: 0
D/niviel: clear loc: 0
D/niviel: after glob: 0
D/niviel: after loc: 0

I just want to clone a local array to a global array.

Edit:

The function is called in the subclass.

requestData(activity, new requestDataCallback() {
    @Override
    public ArrayList<? extends BaseModel> parseDatas(Document document) {
        return RecordProvider.getRecord(activity, document);
    }

@Override
    public void runOnUIThread(ArrayList<? extends BaseModel> datas) {

refreshData((ArrayList<Record>) datas);
    }

});

In your refreshData(), the two lists you use are the same.

protected void refreshData(ArrayList<M> datas) {

Log.d("before glob", String.valueOf(this.datas.size()));
Log.d("before loc", String.valueOf(datas.size()));

here you are clearing datas
this.datas.clear();

so now your datas size will be 0

Log.d("clear glob", String.valueOf(this.datas.size()));
Log.d("clear loc", String.valueOf(datas.size()));

here you are adding it to datas again whose size is already 0
this.datas.addAll(datas);

Log.d("after glob", String.valueOf(this.datas.size()));
Log.d("after loc", String.valueOf(datas.size()));

getAdapter().notifyDataSetChanged();
}