rxjava : functional interface

RxJava/basic/src/_02_functional_interface/FunctionalInterfaceEx_01.java

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+package _02_functional_interface;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.lang.reflect.Array;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.*;
+
+/**
+ * Function  : T -> R
+ * Consumer  : T -> void
+ * Supplier  : void -> T
+ * Operator  : T -> T
+ * Predicate : T -> boolean
+ *
+ */
+public class FunctionalInterfaceEx_01 {
+
+    public static void main(String[] args) {
+
+        // 예외 throw 불가능 -> try catch 구문을 이용하여 예외처리를 한다.
+        Function<BufferedReader, String> f = bufferedReader -> {
+            try {
+                return bufferedReader.readLine();
+            } catch (IOException e) {
+                throw new RuntimeException(e);
+            }
+        };
+
+        // Predicate 사용
+        List<String> list = Arrays.asList("", "test1", "test2", "test3", "");
+        List<String> result = filter(list,  s -> !s.isEmpty()); // 리스트의 공백을 제거하는 predicate 전달
+
+        System.out.println("list = " + list);
+        System.out.println("result = " + result);
+
+        // Consumer 사용
+        List<Integer> list2 = Arrays.asList(1, 2, 3, 4, 5);
+        forEach(list2, i -> System.out.println(i)); // 리스트 값 출력하는 consumer 전달
+
+        // Function 사용
+        List<String> list3 = Arrays.asList("test1", "test22", "test333");
+        List<Integer> result3 = map(list3, s -> s.length()); // 각 요소의 길이 출력
+        System.out.println("result3 = " + result3);
+
+        // Operator 사용
+        UnaryOperator<String> u = str -> str + " test";
+        String result4 = u.apply("operator");
+        System.out.println("result4 = " + result4);
+
+        // Supplier 사용
+        Supplier<String> s = () -> "supplier";
+        String result5 = s.get();
+        System.out.println("result5 = " + result5);
+    }
+
+    public static <T, R> List<R> map(List<T> list, Function<T, R> f) {
+        List<R> result = new ArrayList<>();
+        for (T t : list) {
+            result.add(f.apply(t));
+        }
+        return result;
+    }
+
+    public static <T> void forEach(List<T> list, Consumer<T> c) {
+        for (T t : list) {
+            c.accept(t);
+        }
+    }
+
+    public static <T> List<T> filter(List<T> list, Predicate<T> p) {
+        final List<T> result = new ArrayList<>();
+
+        for (T t : list) {
+            if (p.test(t)) {
+                result.add(t);
+            }
+        }
+        return result;
+    }
+}