java:8:stream

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--- java:8:stream [2019/10/24 10:46]
kwon37xi [unmodifiable, immutable list/set collect]
+++ java:8:stream [2020/08/09 16:06]
kwon37xi
@@ 줄 77: / 줄 77: @@
                                   Collections::unmodifiableList))
 </code>
-  * [[https://www.baeldung.com/java-stream-immutable-collection|Collect a Java Stream to an Immutable Collection]]
+  * [[https://www.baeldung.com/java-stream-immutable-collection|Collect a Java Stream to an Immutable Collection]] [[java:guava|Guava]] 21 부터 Collector 가 추가됨.
+<code java>
+    List<Integer> list = IntStream.range(0, 9)
+      .boxed()
+      .collect(ImmutableList.toImmutableList());
+</code>
+<code java>
+// Generic Immutable Collection collector 만들기. 컬렉션 구현체를 원하는대로 선택
+public static <T, A extends List<T>> Collector<T, A, List<T>> toImmutableList(
+  Supplier<A> supplier) {
+    return Collector.of(
+      supplier,
+      List::add, (left, right) -> {
+        left.addAll(right);
+        return left;
+      }, Collections::unmodifiableList);
+}
+// 사용예 - LinkedList 구현을 unmodifiable로 감싸기
+List<String> givenList = Arrays.asList("a", "b", "c", "d");
+List<String> result = givenList.stream()
+  .collect(MyImmutableListCollector.toImmutableList(LinkedList::new));
+</code>
+  * ''ImmutableMap.toImmutableMap()'' 도 사용가능. ''Collectors.toMap'' 과 유사
 ===== 참고 =====
   * [[https://www.baeldung.com/java-predicate-chain|Java 8 Predicate Chain | Baeldung]]
+  * [[https://www.baeldung.com/java-stream-reduce|Guide to Stream.reduce() | Baeldung]]

java/8/stream.txt · 마지막으로 수정됨: 2022/04/09 00:10 저자 kwon37xi