public String getPostcode(Person person)
{
    if (person != null)
    {
        Address address = person.getAddress();
        if (address != null)
        {
            return address.getPostcode();
        }
    }
    return null;
}

public String getPostcode(Person person)
{
    return person?.getAddress()?.getPostcode();
}

public String getPostcode(Person person) {

    if (person == null) return null;
    Address address = person.getAddress();
    return address != null ? address.getPostcode() : null;
}

if (person != null && person.getAddress() != null)
    return person.getAddress().getPostCode();

public String getPostcode(Person person) {
    return person != null && person.getAddress() != null ? person.getAddress().getPostcode() : null;
}

Address address;
if (person != null && (address = person.getAddress()) != null){
      return address.getPostCode();
}