Sending serial data to Uno via Java. Code works on Uno R3 but not on Mega2560

Projects Interfacing w/ Software on the Computer
3

I dont believe so. Here is a section of a Java code where I establish serial connection (pretty much copied straight from jSSC example posted online);

SerialPort serialPort = new SerialPort("COM10");
        try {
            serialPort.openPort();//Open serial port
            serialPort.setParams(SerialPort.BAUDRATE_9600, 
                                 SerialPort.DATABITS_8,
                                 SerialPort.STOPBITS_1,
                                 SerialPort.PARITY_NONE);//Set params. Also you can set params by this string: serialPort.setParams(9600, 8, 1, 0);
                   
        
        
        }
        catch (SerialPortException ex) {
            System.out.println(ex);
        }

Im pretty sure that Im connecting to the right serial port. My arduino Uno is on "COM8" and Mega is on "COM10" (i verify this in device manager). Before running Java code I modify that very first line. I dont change data bits or stop bits or parity parameters though.

In addition, when I run Java program, the RX LED on the board is flashing..... but nothing is happening. And the code works perfectly with Uno...

Thank you very much for responding! What else could be wrong?