From ac6390da3b7d9851a9ffe5d8e9e1b2cebe37a149 Mon Sep 17 00:00:00 2001
From: Gergo Petrik <petrikgergo@gmail.com>
Date: Wed, 24 Jun 2020 08:16:17 +0200
Subject: [PATCH] Bal 4152 covariant return type (#9561)

* BAEL-4152: added covariant return type material

* BAEL-4152: covariant return type article related code is moved to another package
---
 .../baeldung/covariance/IntegerProducer.java  |  8 +++
 .../com/baeldung/covariance/Producer.java     |  8 +++
 .../CovariantProducersUnitTest.java           | 49 +++++++++++++++++++
 3 files changed, 65 insertions(+)
 create mode 100644 core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/covariance/IntegerProducer.java
 create mode 100644 core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/covariance/Producer.java
 create mode 100644 core-java-modules/core-java-lang-oop-methods/src/test/java/com/baeldung/covariance/CovariantProducersUnitTest.java

diff --git a/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/covariance/IntegerProducer.java b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/covariance/IntegerProducer.java
new file mode 100644
index 0000000000..6a631d45b0
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/covariance/IntegerProducer.java
@@ -0,0 +1,8 @@
+package com.baeldung.covariance;
+
+public class IntegerProducer extends Producer {
+    @Override
+    public Integer produce(String input) {
+        return Integer.parseInt(input);
+    }
+}
diff --git a/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/covariance/Producer.java b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/covariance/Producer.java
new file mode 100644
index 0000000000..94f79ae525
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-methods/src/main/java/com/baeldung/covariance/Producer.java
@@ -0,0 +1,8 @@
+package com.baeldung.covariance;
+
+public class Producer {
+    public Object produce(String input) {
+        Object result = input.toLowerCase();
+        return result;
+    }
+}
diff --git a/core-java-modules/core-java-lang-oop-methods/src/test/java/com/baeldung/covariance/CovariantProducersUnitTest.java b/core-java-modules/core-java-lang-oop-methods/src/test/java/com/baeldung/covariance/CovariantProducersUnitTest.java
new file mode 100644
index 0000000000..2645889ac8
--- /dev/null
+++ b/core-java-modules/core-java-lang-oop-methods/src/test/java/com/baeldung/covariance/CovariantProducersUnitTest.java
@@ -0,0 +1,49 @@
+package com.baeldung.covariance;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class CovariantProducersUnitTest {
+
+    @Test
+    public void whenInputIsArbitrary_thenProducerProducesString() {
+        String arbitraryInput = "just a random text";
+        Producer producer = new Producer();
+
+        Object objectOutput = producer.produce(arbitraryInput);
+
+        assertEquals(arbitraryInput, objectOutput);
+        assertEquals(String.class, objectOutput.getClass());
+    }
+
+    @Test
+    public void whenInputIsArbitrary_thenIntegerProducerFails() {
+        String arbitraryInput = "just a random text";
+        Producer producer = new IntegerProducer();
+
+        assertThrows(NumberFormatException.class, () -> producer.produce(arbitraryInput));
+    }
+
+    @Test
+    public void whenInputIsSupported_thenProducerCreatesInteger() {
+        String integerAsString = "42";
+        Producer producer = new IntegerProducer();
+
+        Object result = producer.produce(integerAsString);
+
+        assertEquals(Integer.class, result.getClass());
+        assertEquals(Integer.parseInt(integerAsString), result);
+    }
+
+    @Test
+    public void whenInputIsSupported_thenIntegerProducerCreatesIntegerWithoutCasting() {
+        String integerAsString = "42";
+        IntegerProducer producer = new IntegerProducer();
+
+        Integer result = producer.produce(integerAsString);
+
+        assertEquals(Integer.parseInt(integerAsString), result);
+    }
+}