ArrayAdapter.ArrayFilter.java

private class ArrayFilter extends Filter {
    @Override
    protected FilterResults performFiltering(CharSequence prefix) {
        
        FilterResults results = new FilterResults();
        if (prefix == null || prefix.length() == 0) {
                ArrayList<T> list;
                synchronized (mLock) {
                    list = new ArrayList<T>(mOriginalValues);
                }
                results.values = list;
                results.count = list.size();
        } else {
            //...
            final ArrayList<T> newValues = new ArrayList<T>();
            
            for (int i = 0; i < count; i++) {
                final T value = values.get(i);
                final String valueText = value.toString().toLowerCase();

                // First match against the whole, non-splitted value
                if (valueText.startsWith(prefixString)) {
                    newValues.add(value);
                } else {
                    //...
                }
            }
        }
        return results;
    }
}