BAEL-1840 Builder Pattern in Kotlin (#4730)

* builder pattern in kotlin

* builder pattern in kotlin new-line

* deleted Sandbox, added unit test

* add other tests

* named and default parameters builder

* Make FoodOrderNamed a data class

core-kotlin/src/main/kotlin/com/baeldung/builder/FoodOrder.kt

@@ -0,0 +1,39 @@
+package com.baeldung.builder
+
+class FoodOrder private constructor(builder: FoodOrder.Builder) {
+
+    val bread: String?
+    val condiments: String?
+    val meat: String?
+    val fish: String?
+
+    init {
+        this.bread = builder.bread
+        this.condiments = builder.condiments
+        this.meat = builder.meat
+        this.fish = builder.fish
+    }
+
+    class Builder {
+
+        var bread: String? = null
+            private set
+        var condiments: String? = null
+            private set
+        var meat: String? = null
+            private set
+        var fish: String? = null
+            private set
+
+        fun bread(bread: String) = apply { this.bread = bread }
+
+        fun condiments(condiments: String) = apply { this.condiments = condiments }
+
+        fun meat(meat: String) = apply { this.meat = meat }
+
+        fun fish(fish: String) = apply { this.fish = fish }
+
+        fun build() = FoodOrder(this)
+
+    }
+}

core-kotlin/src/main/kotlin/com/baeldung/builder/FoodOrderApply.kt

@@ -0,0 +1,8 @@
+package com.baeldung.builder
+
+class FoodOrderApply {
+    var bread: String? = null
+    var condiments: String? = null
+    var meat: String? = null
+    var fish: String? = null
+}

core-kotlin/src/main/kotlin/com/baeldung/builder/FoodOrderNamed.kt

@@ -0,0 +1,7 @@
+package com.baeldung.builder
+
+data class FoodOrderNamed(
+        val bread: String? = null,
+        val condiments: String? = null,
+        val meat: String? = null,
+        val fish: String? = null)

core-kotlin/src/test/kotlin/com/baeldung/builder/BuilderPatternUnitTest.kt

@@ -0,0 +1,139 @@
+package com.baeldung.builder
+
+import org.junit.jupiter.api.Assertions
+import org.junit.jupiter.api.Test
+
+internal class BuilderPatternUnitTest {
+
+    @Test
+    fun whenBuildingFoodOrderSettingValues_thenFieldsNotNull() {
+
+        val foodOrder = FoodOrder.Builder()
+                .bread("white bread")
+                .meat("bacon")
+                .fish("salmon")
+                .condiments("olive oil")
+                .build()
+
+        Assertions.assertNotNull(foodOrder.bread)
+        Assertions.assertNotNull(foodOrder.meat)
+        Assertions.assertNotNull(foodOrder.condiments)
+        Assertions.assertNotNull(foodOrder.fish)
+    }
+
+    @Test
+    fun whenBuildingFoodOrderSettingValues_thenFieldsContainsValues() {
+
+        val foodOrder = FoodOrder.Builder()
+                .bread("white bread")
+                .meat("bacon")
+                .fish("salmon")
+                .condiments("olive oil")
+                .build()
+
+        Assertions.assertEquals("white bread", foodOrder.bread)
+        Assertions.assertEquals("bacon", foodOrder.meat)
+        Assertions.assertEquals("olive oil", foodOrder.condiments)
+        Assertions.assertEquals("salmon", foodOrder.fish)
+    }
+
+    @Test
+    fun whenBuildingFoodOrderWithoutSettingValues_thenFieldsNull() {
+
+        val foodOrder = FoodOrder.Builder()
+                .build()
+
+        Assertions.assertNull(foodOrder.bread)
+        Assertions.assertNull(foodOrder.meat)
+        Assertions.assertNull(foodOrder.condiments)
+        Assertions.assertNull(foodOrder.fish)
+    }
+
+
+    @Test
+    fun whenBuildingFoodOrderNamedSettingValues_thenFieldsNotNull() {
+
+        val foodOrder = FoodOrderNamed(
+                meat = "bacon",
+                fish = "salmon",
+                condiments = "olive oil",
+                bread = "white bread"
+        )
+
+        Assertions.assertNotNull(foodOrder.bread)
+        Assertions.assertNotNull(foodOrder.meat)
+        Assertions.assertNotNull(foodOrder.condiments)
+        Assertions.assertNotNull(foodOrder.fish)
+    }
+
+    @Test
+    fun whenBuildingFoodOrderNamedSettingValues_thenFieldsContainsValues() {
+
+        val foodOrder = FoodOrderNamed(
+                meat = "bacon",
+                fish = "salmon",
+                condiments = "olive oil",
+                bread = "white bread"
+        )
+
+        Assertions.assertEquals("white bread", foodOrder.bread)
+        Assertions.assertEquals("bacon", foodOrder.meat)
+        Assertions.assertEquals("olive oil", foodOrder.condiments)
+        Assertions.assertEquals("salmon", foodOrder.fish)
+    }
+
+    @Test
+    fun whenBuildingFoodOrderNamedWithoutSettingValues_thenFieldsNull() {
+
+        val foodOrder = FoodOrderNamed()
+
+        Assertions.assertNull(foodOrder.bread)
+        Assertions.assertNull(foodOrder.meat)
+        Assertions.assertNull(foodOrder.condiments)
+        Assertions.assertNull(foodOrder.fish)
+    }
+
+    @Test
+    fun whenBuildingFoodOrderApplySettingValues_thenFieldsNotNull() {
+
+        val foodOrder = FoodOrderApply().apply {
+            meat = "bacon"
+            fish = "salmon"
+            condiments = "olive oil"
+            bread = "white bread"
+        }
+
+        Assertions.assertNotNull(foodOrder.bread)
+        Assertions.assertNotNull(foodOrder.meat)
+        Assertions.assertNotNull(foodOrder.condiments)
+        Assertions.assertNotNull(foodOrder.fish)
+    }
+
+    @Test
+    fun whenBuildingFoodOrderApplySettingValues_thenFieldsContainsValues() {
+
+        val foodOrder = FoodOrderApply().apply {
+            meat = "bacon"
+            fish = "salmon"
+            condiments = "olive oil"
+            bread = "white bread"
+        }
+
+        Assertions.assertEquals("white bread", foodOrder.bread)
+        Assertions.assertEquals("bacon", foodOrder.meat)
+        Assertions.assertEquals("olive oil", foodOrder.condiments)
+        Assertions.assertEquals("salmon", foodOrder.fish)
+    }
+
+    @Test
+    fun whenBuildingFoodOrderApplyWithoutSettingValues_thenFieldsNull() {
+
+        val foodOrder = FoodOrderApply()
+
+        Assertions.assertNull(foodOrder.bread)
+        Assertions.assertNull(foodOrder.meat)
+        Assertions.assertNull(foodOrder.condiments)
+        Assertions.assertNull(foodOrder.fish)
+    }
+
+}