civic · April 15, 2014 05:25 · Apr 15, 2014
diff --git a/StreamStudy.java b/StreamStudy.java
@@ -0,0 +1,85 @@
+package java8;
+
+import java.util.Arrays;
+import java.util.EnumSet;
+import java.util.List;
+import java.util.Set;
+import java.util.function.BiConsumer;
+import java.util.function.BinaryOperator;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.stream.Collector;
+import java.util.stream.Stream;
+
+/**
+ * Java8のCollectorをfor文と比較しながら一から作って理解する
+ * @author civic
+ */
+public class StreamStudy {
+
+    public static void main(String[] args) {
+
+        //forでの実装
+        {
+            List<String> list = Arrays.asList("Hello", "World", "Java8", "Stream", "API");
+            StringBuilder buff = new StringBuilder();
+            for (String s: list){
+                if (buff.length() != 0){
+                    buff.append(", ");
+                }
+                buff.append(s);
+            }
+            String commaJoinedString = buff.toString();
+            System.out.println(commaJoinedString);
+        }
+
+
+        //collectorでの実装
+        {
+            Stream<String> stream = Arrays.asList("Hello", "World", "Java8", "Stream", "API").stream();
+
+            String commaJoinedString = stream.parallel().collect(new MyStringJoinCollector());
+            System.out.println(commaJoinedString);
+        }
+
+    }
+
+    private static class MyStringJoinCollector implements Collector<String, StringBuilder, String>{
+
+        @Override
+        public Supplier<StringBuilder> supplier() {
+            return () -> new StringBuilder();
+        }
+
+        @Override
+        public BiConsumer<StringBuilder, String> accumulator() {
+            return (sb, s) -> {
+                if (sb.length() != 0){
+                    sb.append(", ");
+                }
+                sb.append(s);
+            };
+        }
+
+        @Override
+        public BinaryOperator<StringBuilder> combiner() {
+            return (sb1, sb2) ->{
+                if (sb1.length() != 0){
+                    sb1.append(", ");
+                }
+                sb1.append(sb2);
+                return sb1;
+            };
+        }
+
+        @Override
+        public Function<StringBuilder, String> finisher() {
+            return sb -> sb.toString();
+        }
+
+        @Override
+        public Set<Characteristics> characteristics() {
+            return EnumSet.noneOf(Characteristics.class);
+        }
+    }
+}