意識低いプログラマーのJava8入門

本番までに差し替える可能性あり
まだ Java SE 8 を使ったことない人向け

Transcript

1. 1 意識低いプログラマー の Java8 入門 Toast kid (@y_q1m)
2. 2 Disclaimer 2. This slide powered by reveal.js and JavaFX. 3. I don't know Java in Republik Indonesia. 4. This slide licensed . his slide's content is mere my opinion. Eclipse Public License Version 1.0
3. 3 Who are you?
4. 4 Who are you? My name is "Toast kid". I work on Web service company. I like GUI tool. I often use Java SE on work. Storm / Play(1.x) / Spark Framework / Android App
5. 5 I like Java.
6. 6 Qiita Articles @y_q1m 2015/11/29 2016/01/09 2016/04/07 2016/04/09 Eclipse Collections に挑む Java の Pair について考える JavaFX でワードクラウドを作る 声に出して読みたい Java ライブラリ ­filter­
7. 7 About this presentation
8. 8 Target 1. The Java programmer who has not yet used Java8's API. 2. The Android app developper who has not yet used Java8's API. 3. The Java programmer who feels strange to Lambda expression. 4. The programmer who think that Stream API is not useful because for loop is so fantastic.
9. 9 Goal 1. You want to rewrite your codes with Java8 like. 2. You become for­loop prohibition debater.
10. 10 Overview 1. Stream API 2. Conclusion
11. 11 Stream API Everything is a stream.
12. 12 About Stream API For internal iteration We often use it for operating Collection.
13. 13 Stream API's melit for Java developer 1. It can use new Collection operator API. 2. You can write Java source code like natural language. 3. You can parallel processing easily.
14. 14 Stream API's Operators You should learn by heart only 3 operators.
15. 15 filter
16. 16 map
17. 17 forEach
18. 18 operator samples filter select elements map convert elements forEach operate all elements It's similar to RxJava's operators.
19. 19 filter IntStream.range(0, 10) .filter(i ­> {return i % 2 == 0;});
20. 20 map Stream.of("0", "1", "2", "3", "4", "5", "6", "7", "8", "9") .map(i ­> {return Integer.parseInt(i);})
21. 21 forEach IntStream.range(0, 10) .forEach(i ­> {System.out.println(i);});
22. 22 combined operators. Stream.of("0", "1", "2", "3", "4", "5", "6", "7", "8", "9") .map(i ­> {return Integer.parseInt(i);}) .filter(i ­> {return i % 2 == 0;}) .forEach(i ­> {System.out.println(i);});
23. 23 written by former API. final String[] nums = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9" for (final String n : nums) { final int i = Integer.parseInt(n); if (i % 2 == 0) { System.out.println(i); } }
24. 24 Sample
25. 25 Stream API Example Q.全社員のうち、65歳以上の社員が所属するグループの名 前を出力せよ
26. 26 Before Q.全社員のうち、65歳以上の社員が所属するグループの名 前を出力せよ List employees = ...; Set groups = new HashSet<>(); for (Person p : people) { if (p.getAge() >= 65) { groups.add(p.getGroup()); } } for (Group g : groups) { System.out.println(g.getName()); } Oh...Too complex!
27. 27 After Q.全社員のうち、65歳以上の社員が所属するグループの名 前を出力せよ employees .filter(p ­> {return p.getAge() >= 65;}) .map(p ­> {return p.getGroup();}) .forEach(g ­> {System.out.println(g.getName());});
28. 28 What's good?
29. 29 What's good? 1. 余分な変数がない 2. 上から下に読めば何をしたいか明確 3. 必要であればメソッドに切り出せる……テストしやすくなる employees .filter(p ­> {return p.getAge() >= 65;}) .map(p ­> {return p.getGroup();}) .forEach(g ­> {System.out.println(g.getName());});
30. 30 To concurrent な、なんだってー(棒)
31. 31 To concurrent with Lambda & Stream API employees .parallelStream() // add .filter(p ­> {return p.getAge() >= 65;}) .map(p ­> {return p.getGroup();}) .sequential() // add .forEach(g ­> {System.out.println(g.getName());});
32. 32 Problem of Stream API 1. It can't replace all loop code. 2. It's not enough functions. 1. Why don't you use Eclipse Collections! 3. It use more memory than nomal loop code. 4. It can't debug each line.
33. 33 Conclusion
34. 34 Conclusion 1. Stream API をとりあえず使うには filter/map/forEach だ け覚えればなんとかなるよ 2. Stream API 使うと Collection 操作のコードが読みやすく なるよ 3. 標準の Stream API に力不足を感じたら Eclipse Collections を使おう
35. 35 Do you feel it so strange? 変化には必ずコストが伴います。(中略)し かし、Project Lambda による生産性と表 現力の向上は、これらのコストを補って余 りあるはずです 出典：『Java Magazine vol.7』Project Lambda の展望 ­ 言 語アーキテクトのBrian Goetzに聞く(p35­)
36. 36 References 1. 現場で使える 最新 Java SE 7/8 速攻入門 櫻庭 祐一 (著) / 技術評論社 (2015/11/19) 2. Java SE 8のラムダ式はどう実現されたのか？──実装の 経緯、内部的な仕組みを理解する http://builder.japan.zdnet.com/sp_oracle/weblogic/35077771
37. 37 EOP Thank you for listening.