*1단계 - 스트림, 람다, Optional 구현

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

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

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

@@ -53,4 +53,14 @@ public static int sumAllOverThree(List<Integer> numbers) {
         }
         return total;
     }
+
+    public static int sumAllConditional(List<Integer> numbers, Conditional conditional) {
+        int total = 0;
+        for (int number : numbers) {
+            if (conditional.test(number)) {
+                total += number;
+            }
+        }
+        return total;
+    }
 }

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;
 
@@ -15,19 +16,20 @@ 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(word -> word.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(word -> word.length() > 12)
+                .sorted(Comparator.comparing(String::length))
+                .distinct()
+                .reduce("", (total, word) -> total + word + ", ").toLowerCase();
     }
 
     public static List<Integer> doubleNumbers(List<Integer> numbers) {
@@ -39,6 +41,9 @@ public static long sumAll(List<Integer> numbers) {
     }
 
     public static long sumOverThreeAndDouble(List<Integer> numbers) {
-        return 0;
+        return numbers.stream()
+                .filter(number -> number > 3)
+                .map(number -> number * 2)
+                .reduce(0, (total, number) -> total + number);
     }
 }

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 +16,10 @@ 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(expressionData -> matchExpression(expressionData, expression))
+                .findFirst()
+                .orElseThrow(() -> new IllegalArgumentException(String.format("%s는 사칙연산에 해당하지 않는 표현식입니다.", expression)));
     }
 }

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

@@ -1,5 +1,8 @@
 package nextstep.optional;
 
+import java.util.Optional;
+import java.util.stream.Stream;
+
 public class User {
     private String name;
     private Integer age;
@@ -33,7 +36,11 @@ public static boolean ageIsInRange1(User user) {
     }
 
     public static boolean ageIsInRange2(User user) {
-        return false;
+        return Optional.ofNullable(user)
+                .filter(userData -> userData.getAge() != null)
+                .filter(userData -> userData.getAge() >= 30 && userData.getAge() <= 45)
+                .map(userData -> true)
+                .orElse(false);
     }
 
     @Override

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

@@ -2,6 +2,7 @@
 
 import java.util.Arrays;
 import java.util.List;
+import java.util.Optional;
 
 public class Users {
     static final User DEFAULT_USER = new User("codesquad", 100);
@@ -13,11 +14,9 @@ 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));
     }
 }

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