Replacing many if statements

I recently was asked by a colleague how to get rid of a staggering amount of if statements.

They all seem to have remarkable similarities, as is obvious from the code below.

	public List<ValidationMessage> verifyAddress(Address address)
	{
	List<ValidationMessage> messages = new ArrayList<>();
	if (address.getHousenumber() == null)
	{
	messages.add(new ValidationMessage(AddressPart.HOUSENUMBER, "Housenumber is missing"));
	}
	if (address.getHousenumber() != null && (address.getHousenumber() < 0 || address.getHousenumber() > 50000))
	{
	messages.add(new ValidationMessage(AddressPart.HOUSENUMBER, "Housenumber should be between 0 and 50000"));
	}
	if (address.getCity() == null)
	{
	messages.add(new ValidationMessage(AddressPart.CITY, "City is missing"));
	}
	if (address.getStreetName() == null)
	{
	messages.add(new ValidationMessage(AddressPart.STREETNAME, "Streetname is missing"));
	}
	if (address.getState() == null)
	{
	messages.add(new ValidationMessage(AddressPart.STATE, "State is missing"));
	} else if (address.getState().length() != 2)
	{
	messages.add(new ValidationMessage(AddressPart.STATE, "Expecting State to be a 2-letter abbreviation"));
	}
	if (address.getSuffix() != null && address.getSuffix().length() != 1)
	{
	messages.add(new ValidationMessage(AddressPart.SUFFIX, "Suffix to a house number should be just one letter"));
	}
	return messages;
	}

view raw AddressVerifier.java hosted with ❤ by GitHub

So I initially thought about changing it to:

	public List<ValidationMessage> verifyAddress3(Address address)
	{
	Map<Boolean, ValidationMessage> map = new HashMap<>();
	map.put(address.getHousenumber() == null, new ValidationMessage(AddressPart.HOUSENUMBER, "Housenumber is missing"));
	map.put(address.getHousenumber() != null && (address.getHousenumber() < 0 || address.getHousenumber() > 50000),
	new ValidationMessage(AddressPart.HOUSENUMBER, "Housenumber should be between 0 and 50000"));
	map.put(address.getCity() == null, new ValidationMessage(AddressPart.CITY, "City is missing"));
	map.put(address.getStreetName() == null, new ValidationMessage(AddressPart.STREETNAME, "Streetname is missing"));
	map.put(address.getState() == null, new ValidationMessage(AddressPart.STATE, "State is missing"));
	map.put(address.getState() != null && address.getState().length() != 2, new ValidationMessage(AddressPart.STATE, "Expecting State to be a 2-letter abbreviation"));
	map.put(address.getSuffix() != null && address.getSuffix().length() != 1, new ValidationMessage(AddressPart.SUFFIX, "Suffix to a house number should be just one letter"));
	return map.entrySet().stream()
	.filter(Map.Entry::getKey)
	.map(Map.Entry::getValue)
	.collect(Collectors.toList());
	}

view raw AddressVerifier.java hosted with ❤ by GitHub

Of course it is also possible to create a static Map, that contains Functions. That way, the ValidationMessage instances are only created once. It depends on your needs, really.

	private static final Map<Function<Address, Boolean>, ValidationMessage> map = new HashMap<>();
	static
	{
	map.put(address -> address.getHousenumber() == null, new ValidationMessage(AddressPart.HOUSENUMBER, "Housenumber is missing"));
	map.put(address -> address.getHousenumber() != null && (address.getHousenumber() < 0 || address.getHousenumber() > 50000),
	new ValidationMessage(AddressPart.HOUSENUMBER, "Housenumber should be between 0 and 50000"));
	map.put(address -> address.getCity() == null, new ValidationMessage(AddressPart.CITY, "City is missing"));
	map.put(address -> address.getStreetName() == null, new ValidationMessage(AddressPart.STREETNAME, "Streetname is missing"));
	map.put(address -> address.getState() == null, new ValidationMessage(AddressPart.STATE, "State is missing"));
	map.put(address -> address.getState() != null && address.getState().length() != 2, new ValidationMessage(AddressPart.STATE, "Expecting State to be a 2-letter abbreviation"));
	map.put(address -> address.getSuffix() != null && address.getSuffix().length() != 1, new ValidationMessage(AddressPart.SUFFIX, "Suffix to a house number should be just one letter"));
	}
	public List<ValidationMessage> verifyAddress(Address address)
	{
	return map.entrySet().stream()
	.filter((x) -> x.getKey().apply(address))
	.map(Map.Entry::getValue)
	.collect(Collectors.toList());
	}

view raw AddressVerifier.java hosted with ❤ by GitHub

In the end, I don't know if the improvement is really that huge.

It's closer together at least, but I feel it could be improved.