Step1 stream lambda optional

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

@@ -0,0 +1,5 @@
+package nextstep.fp;
+
+public interface Conditional {
+    boolean isMatchedWithCondition(Integer number);
+}

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

@@ -26,28 +26,22 @@ public void run() {
         }).start();
     }
 
-    public static int sumAll(List<Integer> numbers) {
-        int total = 0;
-        for (int number : numbers) {
-            total += number;
-        }
-        return total;
+    public static int sumAll(List<Integer> numbers, Conditional c) {
+        return sum(numbers, c);
     }
 
-    public static int sumAllEven(List<Integer> numbers) {
-        int total = 0;
-        for (int number : numbers) {
-            if (number % 2 == 0) {
-                total += number;
-            }
-        }
-        return total;
+    public static int sumAllEven(List<Integer> numbers, Conditional c) {
+        return sum(numbers, c);
+    }
+
+    public static int sumAllOverThree(List<Integer> numbers, Conditional c) {
+        return sum(numbers, c);
     }
 
-    public static int sumAllOverThree(List<Integer> numbers) {
+    private static int sum(List<Integer> numbers, Conditional c) {
         int total = 0;
         for (int number : numbers) {
-            if (number > 3) {
+            if (c.isMatchedWithCondition(number)) {
                 total += number;
             }
         }

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

@@ -15,19 +15,21 @@ public static long countWords() throws IOException {
                 .get("src/main/resources/fp/war-and-peace.txt")), StandardCharsets.UTF_8);
         List<String> words = Arrays.asList(contents.split("[\\P{L}]+"));
 
-        long count = 0;
-        for (String w : words) {
-            if (w.length() > 12) count++;
-        }
-        return count;
+        return words.stream().filter(v -> v.length() > 12).count();
     }
 
     public static void 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.
+        words.stream()
+                .filter(v -> v.length() > 12)
+                .sorted((a, b) -> b.length() - a.length())
+                .distinct()
+                .collect(Collectors.toList())
+                .subList(0, 100)
+                .forEach(v -> System.out.println(v.toLowerCase()));
     }
 
     public static List<Integer> doubleNumbers(List<Integer> numbers) {
@@ -39,6 +41,6 @@ public static long sumAll(List<Integer> numbers) {
     }
 
     public static long sumOverThreeAndDouble(List<Integer> numbers) {
-        return 0;
+        return numbers.stream().filter(v -> v > 3).map(v -> v * 2).reduce(Integer::sum).orElse(0);
     }
 }

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

@@ -1,5 +1,7 @@
 package nextstep.optional;
 
+import java.util.stream.Stream;
+
 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 Stream.of(values())
+                .filter(v -> matchExpression(v, expression))
+                .findFirst()
+                .orElseThrow(IllegalArgumentException::new);
     }
 }

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 +35,10 @@ public static boolean ageIsInRange1(User user) {
     }
 
     public static boolean ageIsInRange2(User user) {
-        return false;
+        Optional<User> optUser = Optional.ofNullable(user);
+        Optional<Integer> optUserAge = optUser.map(User::getAge).filter(v -> v >= 30).filter(v -> v <= 45);
+
+        return optUserAge.isPresent();
     }
 
     @Override

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

@@ -13,11 +13,6 @@ 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(v -> v.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));
     }
 }

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);
     }
 }