Java Value Types

Transcript

1. Starring With vs Special Appearances by

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3. @hschwentner Value types – The Next Big Thing for Java

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5. #javazone

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13. HENNING

14. @hschwentner SCHWENTNER

15. @hschwentner SHVANTNA

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17. @hschwentner

18. @hshvantna

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23. @hschwentner speakerdeck.com/hschwentner

24. Quelle: http://www.schulbilder.org/malvorlage-informatiker-i10418.html

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27. Fritz & Franz & Lothar & Philipp.

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33. Foto: Kjetil Ree/Wikipedia

34. Foto: Steindy/Wikipedia

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45. Whisky Papa Sierra

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47. ”Enjoyable Business-Software”

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49. ”Enjoyable Business-Software”

50. Value Types for Java

51. @hschwentner DISCLAIMER

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57. Value Types for Java

58. @hschwentner ?

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62. @BrianGoetz

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66. @hschwentner λ

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68. java.util.Optional<T>

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75. @hschwentner “The next big thing for java are value types!”

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77. @hschwentner ?

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87. Identity

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93. @hschwentner Object: *Identity *Lifecycle *(mutable state)

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98. @hschwentner

99. @hschwentner Value: *No identity *immutable

100. @hschwentner Example

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123. 3

124. 3 3

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126. @hschwentner Where does an object live actually?

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134. compile time

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136. run time

137. @hschwentner Where does an object live actually?

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139. 3

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142. int boolean double float

143. unsigned complex

144. iban postcode amount

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146. value-based class

147. @hschwentner Only final fields

148. @hschwentner No state-changing methods

149. @hschwentner equals() does not depend on identity

150. value-based class

151. But

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153. @hschwentner equals() ==

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156. by value

157. by reference

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160. Memory*2

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165. int[]

166. 3 5 10 5 0

167. Object[]

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170. @hschwentner The answer

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173. @hschwentner “Works like an int – codes like a class”

174. @hschwentner Example

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176. y x

177. @hschwentner (x, y)

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182. final __ByValue class Point { private final int _x; private

     final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }

183. final __ByValue class Point { private final int _x; private

     final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }

184. final __ByValue class Point { private final int _x; private

     final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }
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186. final __ByValue class Point { private final int _x; private

     final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }

187. final __ByValue class Point { private final int _x; private

     final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }

188. final __ByValue class Point { private final int _x; private

     final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }

189. final __ByValue class Point { private final int _x; private

     final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }

190. final __ByValue class Point { private final int _x; private

     final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }

191. final __ByValue class Point { private final int _x; private

     final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }

192. final __ByValue class Point { private final int _x; private

     final int _y; public Point(int x, int y) { _x = x; _y = y; } public boolean equals(Point other) { return _x == other._x && _y == other._y; } }

193. @hschwentner “Works like an int – codes like a class”

194. @hschwentner “Works like an int – codes like a class”

195. Point p = __MakeValue(4, 7);

196. Point p = __MakeValue(4, 7);

197. Point p = new Point(4, 7);

198. Point p = Point(4, 7);

199. Point p = (4, 7);

200. 4 7

201. 4 7

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204. 4 7

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206. 4 7

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209. Point p = __MakeValue Point(4, 7);

210. @hschwentner ==

211. @hschwentner !=

212. Default value

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215. @hschwentner What else is there?

216. List<Point>

217. List<int>

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219. List<Point>

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223. Software != End

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225. ?

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229. ✘

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232. Value Object

233. @hschwentner Domain values

234. Postal code GPS coordinate IBAN Container number IATA code Amount

235. Ubiquitous Language

236. Allgegenwärtige Sprache

237. Fach- sprache

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239. Ludwig Wittgenstein “Whereof one cannot speak, thereof one must be

     silent”

240. Ludwig Wittgenstein »Wovon man nicht sprechen kann, darüber muss man

     schweigen.«

241. @hschwentner Example

242. public class BankAccount { private int _balance; public void withdraw(int

     amount) { _balance -= amount; } // ... }

243. public class BankAccount { private int _balance; public void withdraw(int

     amount) { _balance -= amount; } // ... }

244. public class BankAccount { private int _balance; public void withdraw(int

     amount) { _balance -= amount; } // ... }

245. public class BankAccount { private int _balance; public void withdraw(int

     amount) { _balance -= amount; } // ... }

246. public class BankAccount { private int _balance; public void withdraw(int

     amount) { _balance -= amount; } // ... }

247. public class BankAccount { private int _balance; private String _currency;

     public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } }

248. public class BankAccount { private int _balance; private String _currency;

     public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } }

249. public class BankAccount { private int _balance; private String _currency;

     public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } }

250. public class BankAccount { private int _balance; private String _currency;

     public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } }

251. public class BankAccount { private int _balance; private String _currency;

     public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } public void deposit(int amount, String currency) { assert currency.equals(_currency); _balance += amount; } }

252. public class BankAccount { private int _balance; private String _currency;

     public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } public void deposit(int amount, String currency) { assert currency.equals(_currency); _balance += amount; } }

253. public class BankAccount { private int _balance; private String _currency;

     public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } public void deposit(int amount, String currency) { assert currency.equals(_currency); _balance += amount; } }

254. public class BankAccount { private int _balance; private String _currency;

     public void withdraw(int amount, String currency) { assert currency.equals(_currency); _balance -= amount; } public void deposit(int amount, String currency) { assert currency.equals(_currency); _balance += amount; } }

255. public class Amount { private final int _amount; private final

     Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } public Amount add(Amount other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }

256. public class Amount { private final int _amount; private final

     Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } public Amount add(Amount other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }

257. public class Amount { private final int _amount; private final

     Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } public Amount add(Amount other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }

258. public class Amount { private final int _amount; private final

     Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } public Amount add(Amount other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }

259. public class Amount { private final int _amount; private final

     Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } public Amount add(Amount other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }

260. public class Amount { private final int _amount; private final

     Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } public Amount add(Amount other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }

261. public class Amount { private final int _amount; private final

     Currency _currency; public Amount(int amount, Currency currency) { _amount = amount; _currency = currency; } public Amount add(Amount other) { assert hasSameCurrency(other); return new Amount(_amount + other._amount, _currency); } public boolean hasSameCurrency(Amount other) { return other._currency == _currency; } }

262. public class BankAccount { private Amount _balance; public void withdraw(Amount

     amount) { _balance.subtract(amount); } public void deposit(Amount amount) { _balance.add(amount); } }

263. public class BankAccount { private Amount _balance; public void withdraw(Amount

     amount) { _balance.subtract(amount); } public void deposit(Amount amount) { _balance.add(amount); } }

264. public class BankAccount { private Amount _balance; public void withdraw(Amount

     amount) { _balance.subtract(amount); } public void deposit(Amount amount) { _balance.add(amount); } }

265. public class BankAccount { private Amount _balance; public void withdraw(Amount

     amount) { assert amount.isGreaterThan(_amount); _balance.subtract(amount); } public void deposit(Amount amount) { _balance.add(amount); } }

266. Memory*2

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269. ✘

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271. public class Amount { // ... }

272. public __ByValue class Amount { // ... }

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274. public __ByValue class Amount { // ... }

275. @hschwentner eat the cake and have it too

276. @hschwentner real domain models and good performance

277. @hschwentner And in other programming languages?

278. C++

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280. Point p;

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282. Point p = Point(4, 7);

283. 4 7

284. Point * p_pointer;

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286. Point * p_pointer = new Point(4, 7);

287. 4 7

288. Point & p_reference = new Point(4, 7);

289. C++

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291. struct

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297. @hschwentner But

298. @hschwentner Mutable state

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300. Interesting concept: Nullable<T>

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302. Scala

303. Case Class

304. @hschwentner Pattern matching

305. @hschwentner Generated equals() based on the members

306. @hschwentner Immutable

307. value-based class

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309. Data class

310. @hschwentner In the end

311. @hschwentner Key take aways: *value/object are different *domain model and

     performance *only strawman syntax yet
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313. @hschwentner Further Reading

314. project valhalla

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319. Workshop Domain-Driven Design concrete wps.de/ddd

320. • F o t o : H e n n

     i n g S c h w e
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324. @hschwentner FEEDBACK

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329. Henning Schwentner hs@wps.de @hschwentner a