Null-free Extended Address

NicolaisExtendedAddress.java

public class Address {

	// look ma, no comments required

	private final String addressLine;
	private final String city;
	private Optional<String> postcode;

	// nobody has to look at these constructors to check which parameters are
	// allowed to be null because of course none are!

	public Address(String addressLine, String city, Optional<String> postcode) {
		this.addressLine = requireNonNull(addressLine,
				"The argument 'addressLine' must not be null.");
		this.city = requireNonNull(city,
				"The argument 'city' must not be null.");
		this.postcode = requireNonNull(postcode,
				"The argument 'postcode' must not be null.");
	}

	public Address(String addressLine, String city, String postcode) {
		// use 'requireNonNull' inside Optional factory method
		// if you prefer a verbose exception message;
		// otherwise 'Optional.of(postcode)' suffices
		this(addressLine, city, Optional.of(
				requireNonNull(postcode,
						"The argument 'postcode' must not be null.")));
	}

	public Address(String addressLine, String city) {
		this(addressLine, city, Optional.empty());
	}

	// now if some method needs to use the postcode,
	// we can not overlook the fact that it is optional

	public int comparePostcode(Address other) {
		// without Optionals we might overlook that the postcode
		// could be missing and do this:
		// return this.postcode.compareTo(other.postcode);

		if (this.postcode.isPresent() && other.postcode.isPresent())
			return this.postcode.get().compareTo(other.postcode.get());
		else if (this.postcode.isPresent())
			return 1;
		else if (other.postcode.isPresent())
			return -1;
		else
			return 0;
	}

	// of course methods that might not have a result
	// return 'Optional' instead of null

	public static Optional<Address> findAddress(String userInput) {
		// find the address, returning Optional.empty() if not found
	}

	// getters are straight forward and can be generated

	public String getAddressLine() {
		return addressLine;
	}

	public String getCity() {
		return city;
	}

	// look how the field's type matches the getter's type;
	// nice for bean-based code/tools

	public Optional<String> getPostcode() {
		return postcode;
	}

	// in case this 'Address' is mutable
	// (which it probably shouldn't be but let's presume it is)
	// you can decide whether you prefer a setter that takes an 'Optional',
	// a pair of methods to set an existing and an empty postcode, or both

	public void setPostcode(Optional<String> postcode) {
		this.postcode = requireNonNull(postcode,
				"The argument 'postcode' must not be null.");
	}

	public void setPostcode(String postcode) {
		// again you might want to use 'requireNonNull'
		// if you prefer a verbose exception message;
		this.postcode = Optional.of(
				requireNonNull(postcode,
						"The argument 'postcode' must not be null."));
	}

	public void setEmptyPostcode() {
		this.postcode = Optional.empty();
	}

}