# Quick code question about Serial ports

**URL:** https://discourse.processing.org/t/quick-code-question-about-serial-ports/26764
**Category:** Electronics (Arduino, etc.)
**Created:** [January 4, 2021, 8:29am UTC](https://discourse.processing.org/t/quick-code-question-about-serial-ports/26764 "2021-01-04T08:29:24Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![jimlee](https://avatars.discourse-cdn.com/v4/letter/j/8e8cbc/32.png) [@jimlee](https://discourse.processing.org/u/jimlee)
#### Post date: [January 4, 2021, 8:29am UTC](https://discourse.processing.org/t/quick-code-question-about-serial-ports/26764/1 "2021-01-04T08:29:24Z")

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I have a GDropList that I populate with the serial ports on my machine so I can select one. Here’s the code to set up the list…

```auto
// Method to setup the port listing popup selctor thing.
public void setupPortList(GDropList portList) {
   
  int i;
  List<String> ourPortList;
   
  ourPortList = new ArrayList<String>(); // Create the array/list of strings.
  ourPortList.add("No port selected"); // Preload the first string as the "No Port selected" label.
  i = 0; // Set i, our list index to 0;
  while(i<myPort.list().length) { // While our listr index is less than the number of serial ports..
    ourPortList.add(myPort.list()[i++]); // We pop in each serial port name and bump up i.
  }
  portList.setItems(ourPortList,0); // When we show this, set it to show item 0. (The none selcted text)
}

```

And as far as I can tell, this works fine. When it fires up I see No Port selected and there is no port selected.

Then when I select a port…

```auto
public void portList_click(GDropList source, GEvent event) { //_CODE_:portList:775264:
  
  int index = source.getSelectedIndex();
  String portName = Serial.list()[index-1];
  myPort = new Serial(this, portName, 57600);
} //_CODE_:portList:775264:

```

It chooses the port name and sets up my port. This also seems to work fine.

What I get errors on is when I choose a new port. In the c++ world I’d delete the old port and create a new one. But in Java I assumed I just create the new port and I magically get a new port. But it doesn’t seem to work like that. Switch back and forth, I no longer get data. But I see its still going out the hardware.

How is one to change ports?

Thanks!

-jim lee

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<div class="post-metadata">

### Author: ![GoToLoop](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.processing.org/gotoloop/32/86_2.png) [@GoToLoop](https://discourse.processing.org/u/GoToLoop)
#### Post date: [January 4, 2021, 8:43am UTC](https://discourse.processing.org/t/quick-code-question-about-serial-ports/26764/2 "2021-01-04T08:43:19Z")

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I don’t have the hardware to test serial ports but shouldn’t you at least **stop()** your previous Serial instance before instantiating a `new` 1?

> **[stop() / Libraries](https://processing.org/reference/libraries/serial/Serial_stop_.html)**
>
> Stops data communication on this port. Use to shut the connection when you're finished with the Serial.

> [@jimlee](#):
>
> In the c++ world I’d delete the old port and create a new one.

Much probably the Serial library is a wrapper over some code written in C or C++.

That’s why we need to explicitly close/stop an instance of anything that relies on native code.

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### Author: ![jimlee](https://avatars.discourse-cdn.com/v4/letter/j/8e8cbc/32.png) [@jimlee](https://discourse.processing.org/u/jimlee)
#### Post date: [January 4, 2021, 8:55am UTC](https://discourse.processing.org/t/quick-code-question-about-serial-ports/26764/3 "2021-01-04T08:55:45Z")

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Oh! That makes perfect sense! Thanks!

-jim lee