jruby compile warnings

[ioquatix]

mkdir -p tmp/java/nio4r_ext
javac --release=8 -Xlint -d tmp/java/nio4r_ext -cp /home/samuel/.rubies/jruby-9.4.2.0/lib/jruby.jar ext/nio4r/org/nio4r/ByteBuffer.java ext/nio4r/org/nio4r/Monitor.java ext/nio4r/org/nio4r/Nio4r.java ext/nio4r/org/nio4r/Selector.java
ext/nio4r/org/nio4r/ByteBuffer.java:30: warning: [serial] non-transient instance field of a serializable class declared with a non-serializable type
    private java.nio.ByteBuffer byteBuffer;
                                ^
ext/nio4r/org/nio4r/Monitor.java:17: warning: [serial] non-transient instance field of a serializable class declared with a non-serializable type
    private SelectionKey key;
                         ^
ext/nio4r/org/nio4r/Monitor.java:19: warning: [serial] non-transient instance field of a serializable class declared with a non-serializable type
    private IRubyObject interests, selector, value, closed;
                        ^
ext/nio4r/org/nio4r/Monitor.java:19: warning: [serial] non-transient instance field of a serializable class declared with a non-serializable type
    private IRubyObject interests, selector, value, closed;
                                   ^
ext/nio4r/org/nio4r/Monitor.java:19: warning: [serial] non-transient instance field of a serializable class declared with a non-serializable type
    private IRubyObject interests, selector, value, closed;
                                             ^
ext/nio4r/org/nio4r/Monitor.java:19: warning: [serial] non-transient instance field of a serializable class declared with a non-serializable type
    private IRubyObject interests, selector, value, closed;
                                                    ^
ext/nio4r/org/nio4r/Selector.java:237: warning: [deprecation] beforeBlockingCall() in RubyThread has been deprecated
            context.getThread().beforeBlockingCall();
                               ^
ext/nio4r/org/nio4r/Selector.java:25: warning: [serial] non-transient instance field of a serializable class declared with a non-serializable type
    private java.nio.channels.Selector selector;
                                       ^
8 warnings
touch tmp/java/nio4r_ext/.build
jar cf tmp/java/nio4r_ext/nio4r_ext.jar -C tmp/java/nio4r_ext org/nio4r/ByteBuffer.class -C tmp/java/nio4r_ext org/nio4r/Monitor.class -C tmp/java/nio4r_ext org/nio4r/Nio4r\$1.class -C tmp/java/nio4r_ext org/nio4r/Nio4r\$2.class -C tmp/java/nio4r_ext org/nio4r/Nio4r\$3.class -C tmp/java/nio4r_ext org/nio4r/Nio4r.class -C tmp/java/nio4r_ext org/nio4r/Selector.class
install -c tmp/java/nio4r_ext/nio4r_ext.jar lib/nio4r_ext.jar

@headius are you able to help? compiled with java-19-openjdk.