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)