Validate annotation on field when it changed

I have to validate the field when it is changed (both throw setter and reflection) in POJO. And I want to write an annotation to the field. The following code doesn't work:

    public class PriceValidator implements ConstraintValidator<Price, BigDecimal> {
    @Override
    public void initialize(Price contactNumber) {
    }
    @Override
    public boolean isValid(BigDecimal value, ConstraintValidatorContext cxt) {
        if (smtng) {
            {
                //do smtng
            }
        }
        return true;
    }
}

How it can be realized this validator? How I should write the annotation correctly?