SOLVED: Serial monitor input error under Linux

Just starting out with Arduino on a basic keypad sketch.
Version 1.8.13 under Linux
Getting this error when attempting to print a value to the serial monitor:

Exception in thread "EventThread /dev/ttyACM0" java.lang.NoSuchMethodError: java.nio.ByteBuffer.flip()Ljava/nio/ByteBuffer;
at processing.app.Serial.processSerialEvent(Serial.java:210)
at processing.app.Serial.serialEvent(Serial.java:183)
at jssc.SerialPort$LinuxEventThread.run(SerialPort.java:1299)

I have given myself permission to uucp which is the group for /dev/ttyACM0 so that does not appear to be the problem. Any assistance would be appreciated.

EDIT: found solution - inconsistent java pathnames in ArchLinux java jdk as per:

Thanks for the feedback; karma added.