Can I use ArrayList in a class which extends Thread?

Can I use ArrayList in a class which extends Thread?

Is it possible to use an ArrayList within a class that extends Thread? I
have written some code to read from Bluetooth serial which was working,
but I've added an ArrayList to keep track of what I'm reading. However I'm
getting NullPointException on any line that accesses results. I know that
ArrayList is not thread safe (although I may not understand fully what
that means) so I may be trying to do impossible things but I thought I
would check with the experts as ArrayLists are otherwise very easy to work
with.
private class ConnectedThread extends Thread {
private final BluetoothSocket mmSocket;
private final InputStream mmInStream;
private List<String> results;
public ConnectedThread(BluetoothSocket socket) {
Log.d(TAG, "create ConnectedThread");
mmSocket = socket;
InputStream tmpIn = null;
OutputStream tmpOut = null;
List<String> results = new ArrayList<String>();
// Get the BluetoothSocket input and output streams
try {
tmpIn = socket.getInputStream();
tmpOut = socket.getOutputStream();
} catch (IOException e) {
Log.e(TAG, "temp sockets not created", e);
}
mmInStream = tmpIn;
mmOutStream = tmpOut;
init();
}
private void init(){
code = new byte[16];
checksum = 0;
tempbyte = 0;
bytesread = -1;
if(!results.isEmpty()){
Log.i(TAG, "Already have found: " + results.size() + " things.");
}
}
public void run(){
//do things
}
}