checkbox giving NPE eror in android

Hi In this below code I am creating checkbox array named as checkBoxState.But when I am clicking it's giving NPE In the below code.My activity it will show the usernames with checkbox when I am selecting with check box but it's throwing NPE.

Can any one help me. java

boolean checkBoxState[];
public View getView(final int position, View convertView, ViewGroup parent) {

            final ViewHolder holder;


            if (convertView == null) 
            {
                convertView = mInflater.inflate(R.layout.grouplist, null);


                holder = new ViewHolder();

                holder.text = (TextView) convertView.findViewById(R.id.text);
                holder.icon = (ImageView) convertView.findViewById(R.id.icon);
                holder.check1 = (CheckBox) convertView.findViewById(R.id.checkBox1);

                convertView.setTag(holder);

            }           

            else {

                holder = (ViewHolder) convertView.getTag();
            }


            holder.text.setText(friends[position].userName);
            holder.icon.setImageBitmap(friends[position].status == STATUS.ONLINE ? mOnlineIcon : mOfflineIcon);

            holder.check1.setChecked(checkBoxState[position]);
            holder.check1.setOnCheckedChangeListener(new OnCheckedChangeListener(){

                public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                    checkBoxState[position]=isChecked;
                }
            });


            return convertView;
        }