BAEL-1553 (#3679)

core-java/src/main/java/com/baeldung/casting/Animal.java

@@ -0,0 +1,13 @@
+package com.baeldung.casting;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class Animal {
+    private static final Logger LOGGER = LoggerFactory.getLogger(Animal.class);
+
+    public void eat() {
+        LOGGER.info("animal is eating");
+    }
+
+}

core-java/src/main/java/com/baeldung/casting/AnimalFeeder.java

@@ -0,0 +1,23 @@
+package com.baeldung.casting;
+
+import java.util.List;
+
+public class AnimalFeeder {
+
+    public void feed(List<Animal> animals) {
+        animals.forEach(animal -> {
+            animal.eat();
+            if (animal instanceof Cat) {
+                ((Cat) animal).meow();
+            }
+        });
+    }
+
+    public void uncheckedFeed(List<Animal> animals) {
+        animals.forEach(animal -> {
+            animal.eat();
+            ((Cat) animal).meow();
+        });
+    }
+
+}

core-java/src/main/java/com/baeldung/casting/Cat.java

@@ -0,0 +1,16 @@
+package com.baeldung.casting;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class Cat extends Animal implements Mew {
+    private static final Logger LOGGER = LoggerFactory.getLogger(Cat.class);
+
+    public void eat() {
+        LOGGER.info("cat is eating");
+    }
+
+    public void meow() {
+        LOGGER.info("meow");
+    }
+}

core-java/src/main/java/com/baeldung/casting/Dog.java

@@ -0,0 +1,12 @@
+package com.baeldung.casting;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class Dog extends Animal {
+    private static final Logger LOGGER = LoggerFactory.getLogger(Dog.class);
+
+    public void eat() {
+        LOGGER.info("dog is eating");
+    }
+}

core-java/src/main/java/com/baeldung/casting/Mew.java

@@ -0,0 +1,5 @@
+package com.baeldung.casting;
+
+public interface Mew {
+    public void meow();
+}

core-java/src/test/java/com/baeldung/casting/CastingTest.java

@@ -0,0 +1,58 @@
+package com.baeldung.casting;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+import java.util.ArrayList;
+import java.util.List;
+
+public class CastingTest {
+
+    @Test
+    public void whenPrimitiveConverted_thenValueChanged() {
+        double myDouble = 1.1;
+        int myInt = (int) myDouble;
+        assertNotEquals(myDouble, myInt);
+    }
+
+    @Test
+    public void whenUpcast_thenInstanceUnchanged() {
+        Cat cat = new Cat();
+        Animal animal = cat;
+        animal = (Animal) cat;
+        assertTrue(animal instanceof Cat);
+    }
+
+    @Test
+    public void whenUpcastToObject_thenInstanceUnchanged() {
+        Object object = new Animal();
+        assertTrue(object instanceof Animal);
+    }
+
+    @Test
+    public void whenUpcastToInterface_thenInstanceUnchanged() {
+        Mew mew = new Cat();
+        assertTrue(mew instanceof Cat);
+    }
+
+    @Test
+    public void whenUpcastToAnimal_thenOverridenMethodsCalled() {
+        List<Animal> animals = new ArrayList<>();
+        animals.add(new Cat());
+        animals.add(new Dog());
+        new AnimalFeeder().feed(animals);
+    }
+
+    @Test
+    public void whenDowncastToCat_thenMeowIsCalled() {
+        Animal animal = new Cat();
+        ((Cat) animal).meow();
+    }
+
+    @Test(expected = ClassCastException.class)
+    public void whenDownCastWithoutCheck_thenExceptionThrown() {
+        List<Animal> animals = new ArrayList<>();
+        animals.add(new Cat());
+        animals.add(new Dog());
+        new AnimalFeeder().uncheckedFeed(animals);
+    }
+}