NullPointer Exception when Adding one list another List

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http://stackoverflow.com – I want show the list of File different dir in remote Dir i success fully retrieve file List but When i add one List to another List NullPointer Exception raises My code is viewListView=(ListView)findViewById(R.id.listView_viewList); final ProgressDialog progressDialog=new ProgressDialog(this); progressDialog.setTitle("Wait"); progressDialog.setMessage("Connecting..."); progressDialog.show(); new Thread(new Runnable() { @Override public void run() { // TODO Auto-generated method stub String groupList[]={"one","Two","Three","Fou (HowTos)