lukasz.drygala@gmail.com - abstract class vs trait

core-scala/src/main/scala/com/baeldung/scala/abstractclassesvstraits/abstractclasses/GroceryProduct.scala

@@ -0,0 +1,19 @@
+package com.baeldung.scala.abstractclassesvstraits.abstractclasses
+
+abstract class GroceryProduct(sku: String) {
+ val price: Double // abstract field
+ val tax: Double = 0.23 // concrete field
+ def calculateTaxFee(): Double = price * tax // concrete method
+}
+
+abstract class Product {
+ val sku: String
+ val price: Double
+}
+
+abstract class TaxCalculator { self: Product => // self type
+ val tax: Double
+ def calculateTaxFee(): Double = price * tax
+}
+
+class Orange(val sku: String, val price: Double) extends GroceryProduct("40303")

core-scala/src/main/scala/com/baeldung/scala/abstractclassesvstraits/abstractclasses/JavaApple.java

@@ -0,0 +1,11 @@
+package com.baeldung.scala.abstractclassesvstraits.abstractclasses;
+
+public class JavaApple extends GroceryProduct {
+ public JavaApple(String sku) {
+ super(sku);
+ }
+ @Override
+ public double price() {
+ return 100;
+ }
+}

core-scala/src/main/scala/com/baeldung/scala/abstractclassesvstraits/traits/GroceryProduct.scala

@@ -0,0 +1,18 @@
+package com.baeldung.scala.abstractclassesvstraits.traits
+
+trait Product {
+ val sku: String
+ val price: Double
+}
+trait TaxCalculator { self: Product => // self type
+ val tax: Double
+ def calculateTaxFee(): Double = price * tax
+}
+
+trait GroceryProduct extends TaxCalculator with Product
+
+object GroceryProduct {
+ class Orange(val sku: String, val price: Double, val tax: Double)
+ extends TaxCalculator
+ with Product
+}

core-scala/src/main/scala/com/baeldung/scala/abstractclassesvstraits/traits/JavaApple.java

@@ -0,0 +1,23 @@
+package com.baeldung.scala.abstractclassesvstraits.traits;
+
+class JavaApple implements GroceryProduct {
+ @Override
+ public String sku() {
+ return null;
+ }
+
+ @Override
+ public double price() {
+ return 0;
+ }
+
+ @Override
+ public double tax() {
+ return 0;
+ }
+
+ @Override
+ public double calculateTaxFee() {
+ return GroceryProduct.super.calculateTaxFee();
+ }
+}

core-scala/src/test/scala/com/baeldung/scala/abstractclassesvstraits/abstractclasses/GroceryProductUnitTest.scala

@@ -0,0 +1,20 @@
+package com.baeldung.scala.abstractclassesvstraits.abstractclasses
+
+import org.scalatest.{Matchers, WordSpec}
+
+class GroceryProductUnitTest extends WordSpec with Matchers {
+ val orange = new Orange("someSku", 100.0)
+
+ "GroceryProduct" should {
+ "calculate tax fee" in {
+ orange.calculateTaxFee() shouldBe 23.0
+ }
+ }
+ "Class" should {
+ "not extends from multiple abstract classes" in {
+ """class Orange(val sku: String, val price: Double, val tax: Double)
+ | extends TaxCalculator
+ | with Product""".stripMargin shouldNot compile
+ }
+ }
+}

core-scala/src/test/scala/com/baeldung/scala/abstractclassesvstraits/traits/GroceryProductUnitTest.scala

@@ -0,0 +1,18 @@
+package com.baeldung.scala.abstractclassesvstraits.traits
+
+import org.scalatest.{Matchers, WordSpec}
+
+class GroceryProductUnitTest extends WordSpec with Matchers {
+ val orange = new GroceryProduct.Orange("someSku", 100.0, 0.23)
+
+ "GroceryProduct" should {
+ "calculate tax fee" in {
+ orange.calculateTaxFee() shouldBe 23.0
+ }
+ }
+ "Trait" should {
+ "not have constructor" in {
+ """trait Orange(sku: String) {}""" shouldNot compile
+ }
+ }
+}