From 131d291bb413174225ec8d5acef1cbfe0fff1255 Mon Sep 17 00:00:00 2001
From: Haeseong Jeon <seong0428@gmail.com>
Date: Wed, 8 Sep 2021 21:51:19 +0900
Subject: [PATCH] =?UTF-8?q?feat:=20=EC=98=88=EC=A0=9C=20=EC=BD=94=EB=93=9C?=
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---
 .../\355\225\264\354\204\261/Chapter05.md"    | 77 +++++++++++++++++++
 1 file changed, 77 insertions(+)

diff --git "a/chapter05/\355\225\264\354\204\261/Chapter05.md" "b/chapter05/\355\225\264\354\204\261/Chapter05.md"
index 13aff35..c3d4a06 100644
--- "a/chapter05/\355\225\264\354\204\261/Chapter05.md"
+++ "b/chapter05/\355\225\264\354\204\261/Chapter05.md"
@@ -134,4 +134,81 @@ https://johngrib.github.io/wiki/law-of-demeter/
 - 연관관계의 주인은 외래키의 위치와 관련해서 정해야지 비즈니스 중요도로 접근하면 안된다. 
 - 양방향 매핑시에는 무한루프에 빠지지 않게 조심해야한다. 
 
+## 예제 개선해보기
+```kotlin
+class Team (
+    private val members: MutableList<Member>
+) {
+    internal fun add(member: Member) {
+        if (!members.contains(member)) {
+            members.add(member)
+        }
+    }
+    internal fun remove(member: Member) {
+        members.remove(member)
+    }
+}
+
+class Member(
+    var team: Team?
+) {
+    internal fun hasTeam(): Boolean {
+        return team != null
+    }
+    internal fun isIn(team: Team): Boolean {
+        return this.team?.let { it == team } ?: false
+    }
+    internal fun isInOtherTeam(team: Team): Boolean {
+        return hasTeam() && !isIn(team)
+    }
+    internal fun join(team: Team) {
+        this.team = team
+    }
+    internal fun withdraw() {
+        this.team = null
+    }
+}
 
+class JoinService {
+    fun join(
+        member: Member,
+        team: Team
+    ) {
+        if (member.hasTeam()) {
+            throw IllegalStateException()
+        }
+        if (member.isIn(team)) {
+            throw IllegalStateException()
+        }
+        member.join(team)
+        team.add(member)
+    }
+}
+
+class ChangeService(
+    private val joinService: JoinService,  
+    private val withdrawalService: WithdrawalService
+) {
+    fun change(
+        member: Member,
+        team: Team
+    ) {
+        if (member.isInOtherTeam(team)) {
+            withdrawalService.withdraw(member)
+        }
+        joinService.join(member, team)
+    }
+}
+
+class WithdrawalService {
+    fun withdraw(
+        member: Member
+    ) {
+        if (!member.hasTeam()) {
+            throw IllegalStateException()
+        }
+        member.team?.remove(member)
+        member.withdraw()
+    }
+}
+```