How do I write real time data to a csv file using a bufferedwriter

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Java

Arduino

realtime

I have a project where I have used an Arduino ultrasonic sensor and have connected it to a java program which reads the values produced by the Arduino ultrasonic sensor via serial communication, the java program produces a real time chart plotting values that are being read from the Arduino.

I want to save that real time data into a csv file. The following code simply creates a file and stores it where the project is located on my computer and does contain any real time data:

{
            saveButton.setText("Save Data");
            String csvFile = "data.csv";
            File f = new File(csvFile);
            FileWriter writer = new FileWriter(csvFile);    
    }

What am I missing in order to as mentioned previously store the real time data into the csv file?

What I have tried:

Online website tutorials, YouTube video tutorials and example codes found online.