Proper use of volatile variables and synchronized blocks

Question

I am trying to wrap my head in thread safety in java (or in general). I have this class (which, I hope, matches the POJO definition), which should also be compatible with JPA providers:

    public class SomeClass {

        private Object timestampLock = new Object();
        // are "volatile"s necessary?
        private volatile java.sql.Timestamp timestamp;
        private volatile String timestampTimeZoneName;

        private volatile BigDecimal someValue;

        public ZonedDateTime getTimestamp() {
            // is synchronisation necessary here? is this the correct usage?
            synchronized (timestampLock) {
                return ZonedDateTime.ofInstant(timestamp.toInstant(), ZoneId.of(timestampTimeZoneName));
            }
        }

        public void setTimestamp(ZonedDateTime dateTime) {
            // is this the correct usage?
            synchronized (timestampLock) {
                this.timestamp = java.sql.Timestamp.from(dateTime.toInstant());
                this.timestampTimeZoneName = dateTime.getZone().getId();
            }
        }

        // is synchronisation required?
        public BigDecimal getSomeValue() {
            return someValue;
        }

        // is synchronisation required?
        public void setSomeValue(BigDecimal val) {
            someValue = val;
        }
    }

As indicated in the comment lines in the code, it is necessary to determine whether timestamp, and timestampTimeZoneNamehow volatile, and whether to use the tags synchronizedas they should be? Or should I only use the blocks synchronizedand not to determine timestamp, and timestampTimeZoneNamehow volatile? A timestampTimeZoneNamea timestampmust not mistakenly coincide with another timestamp.

This link says

Reading and writing are atomic for all variables declared volatile (including long and double variables)

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Answer 1

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synchronized (timestampLock) {
    this.timestamp = java.sql.Timestamp.from(dateTime.toInstant());
    //CONTEXT SWITCH HERE
    this.timestampTimeZoneName = dateTime.getZone().getId();
}

synchronized (timestampLock) {
    return ZonedDateTime.ofInstant(timestamp.toInstant(), ZoneId.of(timestampTimeZoneName));
}

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Answer 2

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Answer 3

    // is synchronisation required?
    public BigDecimal getSomeValue() {
        return someValue;
    }

    // is synchronisation required?
    public void setSomeValue(BigDecimal val) {
        someValue = val;
    }

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