android示例蓝牙聊天应用程序中此空赋值的目的是什么

Question

I'm just analyzing one of android sample applications - the bluetooth chat: https://developer.android.com/samples/BluetoothChat/project.html . I'm looking at the BluetoothChatService class ( https://developer.android.com/samples/BluetoothChat/src/com.example.android.bluetoothchat/BluetoothChatService.html ), at the connect method. There is such piece of code there:

public synchronized void connect(BluetoothDevice device, boolean secure) {
    Log.d("@@@", "connect to: " + device);
    // Cancel any thread attempting to make a connection
    if (mState == STATE_CONNECTING) {
        if (mConnectThread != null) {
            mConnectThread.cancel();
            mConnectThread = null;
        }
    }
    // Cancel any thread currently running a connection
    if (mConnectedThread != null) {
        mConnectedThread.cancel();
        mConnectedThread = null;
    }
    // Start the thread to connect with the given device
    mConnectThread = new ConnectThread(device, secure);
    mConnectThread.start();
    setState(STATE_CONNECTING);
}

I don't understand what is the purpose of this line:

mConnectThread = null;

It seems this line is useless - anyway, just a few lines later mConnectThread is overwritten with new value.

Answer 1

It is safer to set mConnectThread to null earlier in this code, in case an exception is thrown before it has been set to a new value. This way the old instance is available for garbage collection regardless of whether a new value is assigned.

However, one could certainly argue for a better sequence of actions in this method. Generally you're right, there wouldn't be much point in setting it to null just before assigning a new value.