stream.md

資料流替代方案

RxJava 已經介紹了資料流的概念。如果你不需要 RxJava 提供的執行緒管理、錯誤處理等又覺得 RxJava 不夠輕量。或許你可以採用輕量，只針對資料流的函式庫。

StreamSupport

After:

RefStreams.of("one", "two", "three", "four")
    .filter(e -> e.length() > 3)
    .peek(e -> System.out.println("Filtered value: " + e))
    .map(String::toUpperCase)
    .peek(e -> System.out.println("Mapped value: " + e))
    .collect(Collectors.toList());

After:

public static List<String> getNames(List<User> users) {
    return StreamSupport.stream(users).map(user -> user.name()).collect(Collectors.toList());
}

After:

public static String[] getNames(User[] users) {
    return J8Arrays.stream(users).map(user -> user.name()).toArray(length -> new String[length]);
}

其他方案

• https://github.com/kgmyshin/Marray
• https://github.com/konmik/solid
• https://github.com/goldmansachs/gs-collections
• Agera

特點：

• Marray 可修改
• SolidList 主要以 ImmutableList 出發，所以沒實現修改能力
• SolidList 支援 Parcelable 傳遞
• 知名 gs-collections 不過似乎不夠輕

另外還有其他 Promise 選用:

• Bolt-Android

Collections 資料流

map

Java 8:

List<Integer> list = Arrays.asList(1, 2, 3).stream().map(String::valueOf).collect(Collectors.toList());

javaslang:

List<Integer> list = Stream.of(1, 2, 3).map(String::valueOf).toJavaList();
// or
List<Integer> list = javaslang.collection.List.of(1, 2, 3).map(String::valueOf).toJavaList();

GS-Collections:

List<Integer> list = Lists.mutable.of(1, 2, 3).collect(String::valueOf).toList();
// or lazy
List<Integer> lazyList = Lists.mutable.of(1, 2, 3).asLazy().collect(String::valueOf).toList();

RxJava:

List<Integer> list = Observable.from(Arrays.asList(1, 2, 3)).map(String::valueOf).toList().toBlocking().single();

count

Java 8:

long evens = Arrays.asList(1, 2, 3).stream().filter(each -> each % 2 == 0).count();

javaslang:

long evens = javaslang.collection.List.of(1, 2, 3).filter(each -> each % 2 == 0).count();

GS-Collections:

int evens = Lists.mutable.of(1, 2, 3).count(each -> each % 2 == 0);

RxJava:

int evens = Observable.from(Arrays.asList(1, 2, 3)).filter(each -> each % 2 == 0).count().toBlocking().single();

• io.javaslang:javaslang:2.0.2
• com.goldmansachs:gs-collections:7.0.0

See Also

• https://sourceforge.net/projects/streamsupport/
• https://github.com/yongjhih/streamsupport
• http://verhoevenv.github.io/2015/08/18/fluentiterable-streamsupport-java8.html
• https://github.com/goldmansachs/gs-collections
• http://www.goldmansachs.com/gs-collections/documents/GS%20Collections%20Training%20Session%20and%20Kata%205.0.0.pdf
• https://github.com/javaslang/javaslang