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意識低いプログラマー
の Java8 入門
Toast kid (@y_q1m)
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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
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Who are you?
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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
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I like Java.
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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
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About this
presentation
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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.
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Goal
1. You want to rewrite your codes with Java8 like.
2. You become forloop prohibition debater.
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Overview
1. Stream API
2. Conclusion
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Stream API
Everything is a stream.
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About Stream API
For internal iteration
We often use it for operating Collection.
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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.
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Stream API's Operators
You should learn by heart only 3 operators.
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filter
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map
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forEach
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operator samples
filter select elements
map convert elements
forEach operate all elements
It's similar to RxJava's operators.
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filter
IntStream.range(0, 10)
.filter(i > {return i % 2 == 0;});
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map
Stream.of("0", "1", "2", "3", "4", "5", "6", "7", "8", "9")
.map(i > {return Integer.parseInt(i);})
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forEach
IntStream.range(0, 10)
.forEach(i > {System.out.println(i);});
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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);});
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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);
}
}
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Sample
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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
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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!
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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());});
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What's good?
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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());});
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To concurrent
な、なんだってー(棒)
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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());});
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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.
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Conclusion
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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
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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)
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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
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EOP
Thank you for listening.