[Week1][입문편] 12강 코틀린에서 object 키워드를 다루는 방법 (#2)

임준형/kotlin-grammer/src/lec12/objectANDsingleton/JavaPerson.java

@@ -0,0 +1,17 @@
+package lec12.objectANDsingleton;
+
+public class JavaPerson {
+    private static final int MIN_AGE = 1;
+
+    private String name;
+    private int age;
+
+    private JavaPerson(final String name, final int age) {
+        this.name = name;
+        this.age = age;
+    }
+
+    public static JavaPerson from(final String name) {
+        return new JavaPerson(name, MIN_AGE);
+    }
+}

임준형/kotlin-grammer/src/lec12/objectANDsingleton/JavaSingleton.java

@@ -0,0 +1,12 @@
+package lec12.objectANDsingleton;
+
+public class JavaSingleton {
+    private static final JavaSingleton INSTANCE = new JavaSingleton();
+
+    private JavaSingleton() {
+    }
+
+    public static JavaSingleton getInstance() {
+        return INSTANCE;
+    }
+}

임준형/kotlin-grammer/src/lec12/objectANDsingleton/Log.kt

@@ -0,0 +1,5 @@
+package lec12.objectANDsingleton
+
+interface Log {
+    fun log();
+}

임준형/kotlin-grammer/src/lec12/objectANDsingleton/Person.kt

@@ -0,0 +1,26 @@
+package lec12.objectANDsingleton
+
+class Person private constructor(
+    private var name: String,
+    private var age: Int
+) {
+
+    // static 대신 companion object 사용
+    // const 작성시 컴파일 시에 값이 들어감. 정말 진짜 상수
+    // val 작성시 런타임 시에 값이 들어감.
+    companion object Factory : Log {
+        private const val MIN_AGE = 1
+        fun newBaby(name: String): Person {
+            return Person(name, MIN_AGE)
+        }
+
+        override fun log() {
+            println("나는 Person 클래스 동행 객체에요")
+        }
+    }
+}
+
+// 외부에서 바로 접근 가능
+object Singleton {
+    var a:Int = 0
+}

임준형/kotlin-grammer/src/lec12/staticclass/JavaMain.java

@@ -0,0 +1,23 @@
+package lec12.staticclass;
+
+public class JavaMain {
+
+    public static void main(String[] args) {
+        moveSomething(new Moveable() {
+            @Override
+            public void move() {
+                System.out.println("움직인다");
+            }
+
+            @Override
+            public void fly() {
+                System.out.println("난다");
+            }
+        });
+    }
+
+    private static void moveSomething(Moveable moveable) {
+        moveable.move();
+        moveable.fly();
+    }
+}

임준형/kotlin-grammer/src/lec12/staticclass/Lec12Main.kt

@@ -0,0 +1,22 @@
+package lec12.staticclass
+
+import lec12.objectANDsingleton.Person
+
+fun main() {
+    moveSomething(object : Moveable {
+        override fun move() {
+            println("움직인다")
+        }
+
+        override fun fly() {
+            println("난다")
+        }
+    })
+
+    Person.newBaby("hello")
+}
+
+private fun moveSomething(moveable: Moveable) {
+    moveable.move()
+    moveable.fly()
+}

임준형/kotlin-grammer/src/lec12/staticclass/Moveable.java

@@ -0,0 +1,8 @@
+package lec12.staticclass;
+
+public interface Moveable {
+
+    void move();
+
+    void fly();
+}

임준형/kotlin-grammer/섹션3 코틀린에서의 OOP.md

@@ -156,4 +156,48 @@ class Lec11Main {
         isDirectoryPath("/")
     }
 }
+```
+
+## 12강 코틀린에서 object 키워드를 다루는 방법
+
+Java에서 static 클래스를 Kotlin에선 아래와 같이 `companion object`표현
+
+```kotlin
+companion object Factory : Log {
+    private const val MIN_AGE = 1
+    fun newBaby(name: String): Person {
+        return Person(name, MIN_AGE)
+    }
+
+    @JvmStatic
+    override fun log() {
+        println("나는 Person 클래스 동행 객체에요")
+    }
+}
+```
+
+외부에선 아래와 같이 적용 가능하며 마찬가지로 static import와 유사하게 가능
+
+```kotlin
+Person.newBaby("hello")
+```
+
+Java에서 컴패니언 사용하려면 @JvmStatic을 붙여야함
+
+### 싱글톤
+
+object 키워드 쓰면 끝
+
+### 익명클래스 구현시
+
+```kotlin
+moveSomething(object : Moveable {
+    override fun move() {
+        println("움직인다")
+    }
+
+    override fun fly() {
+        println("난다")
+    }
+})
 ```