DATA ENCAPSULATION


Built-in data types:
	int, float, boolean, char, String, [], List<>, Map<>, Set<>

Ultimately, all of our data is stored using these data types.
However, it is often best to wrap these data types in classes
that provide higher-level, domain-specific abstractions.


1. Primitive Obsession


class PhoneBookEntry {
	private String _name;
	private String _address;
	private String _phoneNumber;
}


class PhoneBookEntry {
	private Name        _name;
	private Address     _address;
	private PhoneNumber _phoneNumber;
}



2. Encapsulating Collections


// NO ABSTRACTION


List<PhoneBookEntry> phoneBook;



// SHOULD WRAP THE DATA STRUCTURE IN A CLASS THAT 
// MODELS THE DOMAIN AND PROVIDES ALL OPERATIONS 
// NEEDED BY THE PROGRAM


class PhoneBook {

	private List<PhoneBookEntry> _entries;
}



We typically need the following operations:
	1. Add
	2. Update
	3. Delete
	4. Data Integrity Enforcement
	5. Iterate
	6. Search
	7. Domain-specific Algorithms


// POOR ABSTRACTION

class PhoneBook {

	private List<PhoneBookEntry> _entries;

	// LAZY way to support Add, Update, Delete, Iterate, Search
	List<PhoneBookEntry> getEntries() {
		return _entries;
	}

	// Domain-specific Algorithms
	...
}


Exposes internal implementation
Provides no data integrity enforcement
Lacks operations needed by the program



class PhoneBook {

	private List<PhoneBookEntry> _entries;

	
	public Result addEntry(PhoneBookEntry entry) { ... }

	public Result updateEntry(PhoneBookEntry before, PhoneBookEntry after) { ... }

	public Result deleteEntry(PhoneBookEntry entry) { ... }
	

	public Iterator<PhoneBookEntry> findAll() { ... }

	public PhoneBookEntry findByPhoneNumber(PhoneNumber value) { ... }

	public Iterator<PhoneBookEntry> findByName(Name value) { ... }

	public Iterator<PhoneBookEntry> findByAddress(Address value) { ... }


	// Domain-specific Algorithms
	...
}



// Read-Only Search Results

class PhoneBook {

	private List<PhoneBookEntry> _entries;

	
	public Result addEntry(PhoneBookEntry entry) { ... }

	public Result updateEntry(PhoneBookEntry before, PhoneBookEntry after) { ... }

	public Result deleteEntry(PhoneBookEntry entry) { ... }
	
	//***
	public Iterator<PhoneBookEntry> findAll() { 
		return _entries.iterator();
	}

	OR

	public Iterator<PhoneBookEntry> findAll() {
		return java.util.Collections.unmodifiableList(_entries).iterator();
	}
	//***

	public PhoneBookEntry findByPhoneNumber(PhoneNumber value) { ... }

	public Iterator<PhoneBookEntry> findByName(Name value) { ... }

	public Iterator<PhoneBookEntry> findByAddress(Address value) { ... }


	// Domain-specific Algorithms
	...
}


Indexing


class PhoneBook {

	private List<PhoneBookEntry> _entries;
	private Map<PhoneNumber, PhoneBookEntry> _indexByPhoneNumber;
	private Map<Name, List<PhoneBookEntry>> _indexByName;
	private Map<Address, List<PhoneBookEntry>> _indexByAddress;

	
	public Result addEntry(PhoneBookEntry entry) { ... }

	public Result updateEntry(PhoneBookEntry before, PhoneBookEntry after) { ... }

	public Result deleteEntry(PhoneBookEntry entry) { ... }
	

	public Iterator<PhoneBookEntry> findAll() { ... }

	public PhoneBookEntry findByPhoneNumber(PhoneNumber value) { ... }

	public Iterator<PhoneBookEntry> findByName(Name value) { ... }

	public Iterator<PhoneBookEntry> findByAddress(Address value) { ... }


	// Domain-specific Algorithms
	...
}



Enable/Disable



class PhoneBook {

	private List<PhoneBookEntry> _entries;
	private Map<PhoneNumber, PhoneBookEntry> _indexByPhoneNumber;
	private Map<Name, List<PhoneBookEntry>> _indexByName;
	private Map<Address, List<PhoneBookEntry>> _indexByAddress;

	
	public Result canAddEntry(PhoneBookEntry entry) { ... }

	public Result addEntry(PhoneBookEntry entry) {
		Result result = canAddEntry(entry);
		if (result.getStatus() == false) {
			return result;
		}
		else {
			...
		}
	}


	public Result canUpdateEntry(PhoneBookEntry before, PhoneBookEntry after) { ... }

	public Result updateEntry(PhoneBookEntry before, PhoneBookEntry after){
		Result result = canUpdateEntry(before, after);
		if (result.getStatus() == false) {
			return result;
		}
		else {
			...
		}
	}


	public Result canDeleteEntry(PhoneBookEntry entry) { ... }

	public Result deleteEntry(PhoneBookEntry entry) {
		Result result = canDeleteEntry(entry);
		if (result.getStatus() == false) {
			return result;
		}
		else {
			...
		}
	}
	

	public Iterator<PhoneBookEntry> findAll() { ... }

	public PhoneBookEntry findByPhoneNumber(PhoneNumber value) { ... }

	public Iterator<PhoneBookEntry> findByName(Name value) { ... }

	public Iterator<PhoneBookEntry> findByAddress(Address value) { ... }


	// Domain-specific Algorithms
	...
}