🚀 1단계 - 스트림, 람다, Optional

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

@@ -18,39 +18,30 @@ 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(() -> System.out.println("Hello from thread")).start();
     }
 
     public static int sumAll(List<Integer> numbers) {
-        int total = 0;
-        for (int number : numbers) {
-            total += number;
-        }
-        return total;
+        return sum(numbers, it -> true);
     }
 
     public static int sumAllEven(List<Integer> numbers) {
-        int total = 0;
-        for (int number : numbers) {
-            if (number % 2 == 0) {
-                total += number;
-            }
-        }
-        return total;
+        return sum(numbers, it -> it % 2 == 0);
     }
 
     public static int sumAllOverThree(List<Integer> numbers) {
-        int total = 0;
-        for (int number : numbers) {
-            if (number > 3) {
-                total += number;
-            }
-        }
-        return total;
+        return sum(numbers, it -> it > 3);
+    }
+
+    public static int sum(List<Integer> numbers, Conditional condition) {
+        return numbers.stream()
+                .filter(condition::test)
+                .mapToInt(Integer::intValue)
+                .sum();
+    }
+
+    @FunctionalInterface
+    public interface Conditional {
+        boolean test(Integer number);
     }
 }

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

@@ -28,6 +28,12 @@ public static void printLongestWordTop100() throws IOException {
         List<String> words = Arrays.asList(contents.split("[\\P{L}]+"));
 
         // TODO 이 부분에 구현한다.
+        words.stream()
+                .filter(word -> word.length() > 12)
+                .sorted((a, b) -> b.length() - a.length())
+                .distinct()
+                .limit(100)
+                .forEach(System.out::println);
     }
 
     public static List<Integer> doubleNumbers(List<Integer> numbers) {
@@ -39,6 +45,6 @@ public static long sumAll(List<Integer> numbers) {
     }
 
     public static long sumOverThreeAndDouble(List<Integer> numbers) {
-        return 0;
+        return numbers.stream().filter(it -> it > 3).map(it -> it * 2).reduce(0, Integer::sum);
     }
 }

src/main/java/nextstep/optional/Expression.java

@@ -1,5 +1,7 @@
 package nextstep.optional;
 
+import java.util.Arrays;
+
 enum Expression {
     PLUS("+"), MINUS("-"), TIMES("*"), DIVIDE("/");
 
@@ -14,12 +16,9 @@ private static boolean matchExpression(Expression e, String expression) {
     }
 
     static Expression of(String expression) {
-        for (Expression v : values()) {
-            if (matchExpression(v, expression)) {
-                return v;
-            }
-        }
-
-        throw new IllegalArgumentException(String.format("%s는 사칙연산에 해당하지 않는 표현식입니다.", expression));
+        return Arrays.stream(values())
+                .filter(e -> matchExpression(e, expression))
+                .findAny()
+                .orElseThrow(() -> new IllegalArgumentException(String.format("%s는 사칙연산에 해당하지 않는 표현식입니다.", expression)));
     }
 }

src/main/java/nextstep/optional/User.java

@@ -1,5 +1,7 @@
 package nextstep.optional;
 
+import java.util.Optional;
+
 public class User {
     private String name;
     private Integer age;
@@ -33,7 +35,11 @@ public static boolean ageIsInRange1(User user) {
     }
 
     public static boolean ageIsInRange2(User user) {
-        return false;
+        return Optional.ofNullable(user)
+                .filter(it -> it.getAge() != null)
+                .filter(it -> it.getAge() >= 30)
+                .filter(it -> it.getAge() <= 45)
+                .isPresent();
     }
 
     @Override

src/main/java/nextstep/optional/Users.java

@@ -13,11 +13,9 @@ public class Users {
             new User("honux", 45));
 
     User getUser(String name) {
-        for (User user : users) {
-            if (user.matchName(name)) {
-                return user;
-            }
-        }
-        return DEFAULT_USER;
+        return users.stream()
+                    .filter(user -> user.matchName(name))
+                    .findFirst()
+                    .orElse(DEFAULT_USER);
     }
 }

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

@@ -8,24 +8,14 @@ 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(() -> true);
         assertThat(actual).isEqualTo(new Car("pobi", 1));
     }
 
     @Test
     public void 정지() {
         Car car = new Car("pobi", 0);
-        Car actual = car.move(new MoveStrategy() {
-            @Override
-            public boolean isMovable() {
-                return false;
-            }
-        });
+        Car actual = car.move(() -> false);
         assertThat(actual).isEqualTo(new Car("pobi", 0));
     }
 }