파라미터가 없는 익명함수 람다식으로 변경

src/main/java/nextstep/fp/Conditional.java

@@ -0,0 +1,6 @@
+package nextstep.fp;
+
+@FunctionalInterface
+public interface Conditional {
+    abstract boolean test(Integer number);
+}

src/main/java/nextstep/fp/Lambda.java

@@ -1,8 +1,10 @@
 package nextstep.fp;
 
 import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
-public class Lambda {
+public class Lambda implements Conditional{
     public static void printAllOld(List<Integer> numbers) {
         System.out.println("printAllOld");
 
@@ -18,23 +20,26 @@ public static void printAllLambda(List<Integer> numbers) {
     }
 
     public static void runThread() {
-        new Thread(new Runnable() {
-            @Override
-            public void run() {
-                System.out.println("Hello from thread");
-            }
-        }).start();
+//        new Thread(new Runnable() {
+//            @Override
+//            public void run() {
+//                System.out.println("Hello from thread");
+//            }
+//        }).start();
+        // 추상메서드(abstract method) 가 한개인 Runnable 인터페이스를 파라미터로 받아 생성하는 Thread를 람다식으로 변경
+        new Thread(() -> System.out.println("Hello from thread"));
     }
 
-    public static int sumAll(List<Integer> numbers) {
+    public static int sumAll(List<Integer> numbers,Conditional conditional) {
         int total = 0;
         for (int number : numbers) {
             total += number;
         }
+
         return total;
     }
 
-    public static int sumAllEven(List<Integer> numbers) {
+    public static int sumAllEven(List<Integer> numbers,Conditional conditional) {
         int total = 0;
         for (int number : numbers) {
             if (number % 2 == 0) {
@@ -44,13 +49,19 @@ public static int sumAllEven(List<Integer> numbers) {
         return total;
     }
 
-    public static int sumAllOverThree(List<Integer> numbers) {
+    public static int sumAllOverThree(List<Integer> numbers, Conditional conditional) {
         int total = 0;
         for (int number : numbers) {
             if (number > 3) {
                 total += number;
             }
         }
+
         return total;
     }
+
+    @Override
+    public boolean test(Integer number) {
+        return false;
+    }
 }

src/main/java/nextstep/fp/StreamStudy.java

@@ -5,6 +5,7 @@
 import java.nio.file.Files;
 import java.nio.file.Paths;
 import java.util.Arrays;
+import java.util.Comparator;
 import java.util.List;
 import java.util.stream.Collectors;
 
@@ -16,18 +17,28 @@ public static long countWords() throws IOException {
         List<String> words = Arrays.asList(contents.split("[\\P{L}]+"));
 
         long count = 0;
-        for (String w : words) {
-            if (w.length() > 12) count++;
-        }
+//        for (String w : words) {
+//            if (w.length() > 12) count++;
+//        }
+        count = words.stream().filter(word -> word.length() > 12 ).count();
         return count;
     }
 
-    public static void printLongestWordTop100() throws IOException {
+    public static List<String> printLongestWordTop100() throws IOException {
         String contents = new String(Files.readAllBytes(Paths
                 .get("src/main/resources/fp/war-and-peace.txt")), StandardCharsets.UTF_8);
         List<String> words = Arrays.asList(contents.split("[\\P{L}]+"));
 
         // TODO 이 부분에 구현한다.
+        List<String> longestSortedWordsTop100 = words.stream()
+                .distinct()
+                .filter(word -> word.length() > 12)
+                .sorted((a,b) -> {return b.length() - a.length();})
+                .limit(100)
+                .map(word -> word.toLowerCase())
+                .collect(Collectors.toList());
+
+        return longestSortedWordsTop100;
     }
 
     public static List<Integer> doubleNumbers(List<Integer> numbers) {
@@ -39,6 +50,11 @@ public static long sumAll(List<Integer> numbers) {
     }
 
     public static long sumOverThreeAndDouble(List<Integer> numbers) {
-        return 0;
+        long result = numbers.stream()
+                .filter(number -> number > 3)
+                .map(number -> number * 2)
+                .reduce(0, (x, y) -> x + y);
+
+        return result;
     }
 }

src/test/java/nextstep/fp/CarTest.java

@@ -8,13 +8,18 @@ public class CarTest {
     @Test
     public void 이동() {
         Car car = new Car("pobi", 0);
-        Car actual = car.move(new MoveStrategy() {
-            @Override
-            public boolean isMovable() {
-                return true;
-            }
+//        Car actual = car.move(new MoveStrategy() {
+//            @Override
+//            public boolean isMovable() {
+//                return true;
+//            }
+//        });
+
+        Car lambdaCar = car.move(() ->{
+            return true;
         });
-        assertThat(actual).isEqualTo(new Car("pobi", 1));
+
+        assertThat(lambdaCar).isEqualTo(new Car("pobi", 1));
     }
 
     @Test
@@ -26,6 +31,9 @@ public boolean isMovable() {
                 return false;
             }
         });
-        assertThat(actual).isEqualTo(new Car("pobi", 0));
+
+        Car lambdaCar = car.move(() -> {return false;});
+
+        assertThat(lambdaCar).isEqualTo(new Car("pobi", 0));
     }
 }

src/test/java/nextstep/fp/LambdaTest.java

@@ -33,19 +33,19 @@ public void runThread() throws Exception {
 
     @Test
     public void sumAll() throws Exception {
-        int sum = Lambda.sumAll(numbers);
+        int sum = Lambda.sumAll(numbers,(number) -> true);
         assertThat(sum).isEqualTo(21);
     }
 
     @Test
     public void sumAllEven() throws Exception {
-        int sum = Lambda.sumAllEven(numbers);
+        int sum = Lambda.sumAllEven(numbers,(number -> number %2 ==0));
         assertThat(sum).isEqualTo(12);
     }
 
     @Test
     public void sumAllOverThree() throws Exception {
-        int sum = Lambda.sumAllOverThree(numbers);
+        int sum = Lambda.sumAllOverThree(numbers, (number) -> number > 3);
         assertThat(sum).isEqualTo(15);
     }
 }

src/test/java/nextstep/fp/StreamStudyTest.java

@@ -24,7 +24,8 @@ public void countWords() throws Exception {
 
     @Test
     public void printLongestWordTop100() throws Exception {
-        StreamStudy.printLongestWordTop100();
+        List<String> top100Words = StreamStudy.printLongestWordTop100();
+        top100Words.forEach(System.out::println);
     }
 
     @Test