feat : Design Pattern - 널 객체(Null Object) 패턴 구현

놀이터(예제 코드 작성)/solid-design-pattern-sample/README.md

@@ -156,7 +156,13 @@
 - 프랜차이즈 기업은 이름을 갖는다.
 - 프랜차이즈 가맹점은 이름을 갖는다.
 
-### 널(Null) 객체 패턴
+### 널 객체(Null Object) 패턴
+
+#### 구현 요구사항
+
+- 식당에서는 직원을 이름으로 관리하며 동명이인은 없다고 가정한다.
+- 이름으로 직원을 찾을 수 있고, 해당 직원에게 근무일자를 할당할 수 있다.
+- 직원은 근무일자를 고지 받으면 해당 날짜를 기억한다.
 
 ## 참고자료
 

놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/nill/after/Employee.kt

@@ -0,0 +1,23 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.nill.after
+
+interface Employee {
+    companion object {
+        val NOT_FOUND = object : Employee {
+            override val name: String
+                get() = "존재하지 않음"
+
+            override fun memorizeWorkingDays(workingDays: List<Int>) {
+                // 아무 작업도 하지 않는다.
+            }
+        }
+    }
+
+    val name: String
+    var workingDays: List<Int>
+        get() = listOf()
+        set(workingDays) {
+            memorizeWorkingDays(workingDays)
+        }
+
+    fun memorizeWorkingDays(workingDays: List<Int>)
+}

놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/nill/after/Restaurant.kt

@@ -0,0 +1,28 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.nill.after
+
+class Restaurant(
+    private val employees: MutableList<Employee> = mutableListOf()
+) {
+    fun addEmployee(employee: Employee) {
+        employees.add(employee)
+    }
+
+    fun removeEmployee(employee: Employee) {
+        employees.remove(employee)
+    }
+
+    fun showAllEmployeesWorkingDays() {
+        for (employee in employees) {
+            println("${employee.name}의 근무일은 ${employee.workingDays}일 입니다.")
+        }
+    }
+
+    fun assignWorkingDays(workingDays: List<Int>, employeeName: String) {
+        val employee = findEmployee(employeeName)
+        employee.memorizeWorkingDays(workingDays)
+    }
+
+    private fun findEmployee(employeeName: String): Employee {
+        return employees.find { it.name == employeeName } ?: Employee.NOT_FOUND
+    }
+}

놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/nill/after/RestaurantApplication.kt

@@ -0,0 +1,13 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.nill.after
+
+class RestaurantApplication
+
+fun main() {
+    val restaurant = Restaurant()
+    restaurant.addEmployee(WorkingEmployee("banjjoknim"))
+
+    restaurant.assignWorkingDays(listOf(1, 4, 7, 14, 20, 27), "banjjoknim")
+    restaurant.assignWorkingDays(listOf(2, 5, 10, 17, 23, 29), "colt")
+
+    restaurant.showAllEmployeesWorkingDays()
+}

놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/nill/after/WorkingEmployee.kt

@@ -0,0 +1,10 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.nill.after
+
+class WorkingEmployee(
+    override val name: String,
+    override var workingDays: List<Int> = listOf()
+) : Employee {
+    override fun memorizeWorkingDays(workingDays: List<Int>) {
+        this.workingDays = workingDays
+    }
+}

놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/nill/before/Employee.kt

@@ -0,0 +1,25 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.nill.before
+
+class Employee(
+    val name: String,
+    var workingDays: List<Int> = listOf()
+) {
+    fun memorizeWorkingDays(workingDays: List<Int>) {
+        this.workingDays = workingDays
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other) return true
+        if (javaClass != other?.javaClass) return false
+
+        other as Employee
+
+        if (name != other.name) return false
+
+        return true
+    }
+
+    override fun hashCode(): Int {
+        return name.hashCode()
+    }
+}

놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/nill/before/Restaurant.kt

@@ -0,0 +1,30 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.nill.before
+
+class Restaurant(
+    private val employees: MutableList<Employee> = mutableListOf()
+) {
+    fun addEmployee(employee: Employee) {
+        employees.add(employee)
+    }
+
+    fun removeEmployee(employee: Employee) {
+        employees.remove(employee)
+    }
+
+    fun showAllEmployeesWorkingDays() {
+        for (employee in employees) {
+            println("${employee.name}의 근무일은 ${employee.workingDays}일 입니다.")
+        }
+    }
+
+    fun assignWorkingDays(workingDays: List<Int>, employeeName: String) {
+        val employee = findEmployee(employeeName)
+        if (employee != null) {
+            employee.memorizeWorkingDays(workingDays)
+        }
+    }
+
+    private fun findEmployee(employeeName: String): Employee? {
+        return employees.find { it.name == employeeName }
+    }
+}

놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/nill/before/RestaurantApplication.kt

@@ -0,0 +1,13 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.nill.before
+
+class RestaurantApplication
+
+fun main() {
+    val restaurant = Restaurant()
+    restaurant.addEmployee(Employee("banjjoknim"))
+
+    restaurant.assignWorkingDays(listOf(1, 4, 7, 14, 20, 27), "banjjoknim")
+    restaurant.assignWorkingDays(listOf(2, 5, 10, 17, 23, 29), "colt")
+
+    restaurant.showAllEmployeesWorkingDays()
+}