rxjava : stream

RxJava/basic/src/_03_stream/Dish.java

@@ -0,0 +1,55 @@
+package _03_stream;
+
+import java.util.Arrays;
+import java.util.List;
+
+public class Dish {
+
+    private final String name;
+    private final boolean vegetarian;
+    private final int calories;
+    private final Type type;
+
+    public Dish(String name, boolean vegetarian, int calories, Type type) {
+        this.name = name;
+        this.vegetarian = vegetarian;
+        this.calories = calories;
+        this.type = type;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public boolean isVegetarian() {
+        return vegetarian;
+    }
+
+    public int getCalories() {
+        return calories;
+    }
+
+    public Type getType() {
+        return type;
+    }
+
+    public enum Type {
+        MEAT, FISH, OTHER
+    }
+
+    @Override
+    public String toString() {
+        return name;
+    }
+
+    public static final List<Dish> menu = Arrays.asList(
+            new Dish("돼지고기", false, 800, Type.MEAT),
+            new Dish("소고기", false, 700, Type.MEAT),
+            new Dish("닭고기", false, 400, Type.MEAT),
+            new Dish("감자 튀김", true, 530, Type.OTHER),
+            new Dish("밥", true, 350, Type.OTHER),
+            new Dish("계절 과일", true, 120, Type.OTHER),
+            new Dish("피자", true, 550, Type.OTHER),
+            new Dish("연어", false, 450, Type.FISH)
+    );
+}

RxJava/basic/src/_03_stream/StreamEx_01.java

@@ -0,0 +1,28 @@
+package _03_stream;
+
+import java.util.Arrays;
+
+public class StreamEx_01 {
+
+    public static void main(String[] args) {
+
+        String[] words = {"a", "bc", "def"};
+
+        // stream 사용 X
+        int count = 0;
+        for (String word : words) {
+            if (word.length() > 2) {
+                count++;
+            }
+        }
+
+        System.out.println("count = " + count);
+
+        // stream 사용
+        long streamCount = Arrays.stream(words)
+                .filter(word -> word.length() > 2)
+                .count();
+
+        System.out.println("streamCount = " + streamCount);
+    }
+}

RxJava/basic/src/_03_stream/StreamEx_02.java

@@ -0,0 +1,21 @@
+package _03_stream;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Random;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+public class StreamEx_02 {
+
+    public static void main(String[] args) {
+
+        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
+
+        // 스트림 생성
+        Stream<Integer> stream = list.stream(); // Collection
+        Stream<String> stringStream = Stream.of("a", "b", "c");// 배열
+        Stream<Double> ranStream = Stream.generate(Math::random); // 메소드 레퍼런스
+        IntStream intStream = new Random().ints(5); // 난수 스트림
+    }
+}

RxJava/basic/src/_03_stream/StreamEx_03.java

@@ -0,0 +1,26 @@
+package _03_stream;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Stream;
+
+public class StreamEx_03 {
+
+    public static void main(String[] args) {
+
+        List<Integer> list = Arrays.asList(3, 1, 5, 4, 2);
+        List<Integer> sortedList = list.stream()
+                .sorted()  // 정렬
+                .toList(); // 새로운 List 에 저장
+
+        System.out.println("list = " + list);
+        System.out.println("sortedList = " + sortedList);
+
+        String[] words = {"a", "bc", "def"};
+
+        Stream<String> stream = Arrays.stream(words);
+        stream.forEach(System.out::println);
+//        long count = stream.count(); // 재사용 불가
+//        System.out.println("count = " + count);
+    }
+}

RxJava/basic/src/_03_stream/StreamEx_04.java

@@ -0,0 +1,15 @@
+package _03_stream;
+
+import java.util.stream.Stream;
+
+public class StreamEx_04 {
+
+    public static void main(String[] args) {
+
+        Stream<String> stringStream = Stream.of("aa", "bb", "cc", "dd", "ee");
+        int sum = stringStream.parallel() // 병렬 스트림으로 전환
+                .mapToInt(String::length).sum();
+        System.out.println("sum = " + sum);
+
+    }
+}

RxJava/basic/src/_03_stream/StreamEx_05.java

@@ -0,0 +1,17 @@
+package _03_stream;
+
+import java.util.List;
+
+public class StreamEx_05 {
+
+    public static void main(String[] args) {
+
+        List<String> names = Dish.menu.stream()
+                .filter(dish -> dish.getCalories() > 300)
+                .map(Dish::getName)
+                .limit(3)
+                .toList();
+
+        System.out.println("names = " + names);
+    }
+}