diff --git a/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Animal.java b/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Animal.java new file mode 100644 index 0000000000..b57f68f053 --- /dev/null +++ b/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Animal.java @@ -0,0 +1,6 @@ +package com.baeldung.exceptions.classcastexception; + +public interface Animal { + + String getName(); +} diff --git a/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Box.java b/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Box.java new file mode 100644 index 0000000000..bb67407218 --- /dev/null +++ b/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Box.java @@ -0,0 +1,14 @@ +package com.baeldung.exceptions.classcastexception; + +public class Box { + + private T content; + + public T getContent() { + return content; + } + + public void setContent(T content) { + this.content = content; + } +} diff --git a/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Frog.java b/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Frog.java new file mode 100644 index 0000000000..0a0b2d1f63 --- /dev/null +++ b/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Frog.java @@ -0,0 +1,9 @@ +package com.baeldung.exceptions.classcastexception; + +public class Frog extends Reptile { + + @Override + public String getName() { + return super.getName() + ": Frog"; + } +} diff --git a/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Main.java b/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Main.java deleted file mode 100644 index a92c9c6d74..0000000000 --- a/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Main.java +++ /dev/null @@ -1,94 +0,0 @@ -package com.baeldung.exceptions.classcastexception; - -import java.io.Serializable; - -public class Main { - - public static void main(String[] args) { - checkedCasts(); - uncheckedConversion(); - genericConversion(); - } - - private static void checkedCasts() { - Animal animal = new Frog(); - try { - Mammal mammal = (Mammal) animal; - } catch (ClassCastException e) { - System.out.println("A checked downcast to Mammal is incompatible from Frog because Frog is not a subtype of Mammal."); - } - - try { - Serializable serial = (Serializable) animal; - } catch (ClassCastException e) { - System.out.println("A checked cast to Serializable is incompatible from Frog because Frog is not a subtype of Serializable."); - } - - Object primitives = new int[1]; - try { - Integer[] integers = (Integer[]) primitives; - } catch (ClassCastException e) { - System.out.println("A checked cast to Integer[] is incompatible from primitive arrays. Auto-boxing does not work for arrays."); - } - - try { - long[] longs = (long[]) primitives; - } catch (ClassCastException e) { - System.out.println("A checked cast to long[] is incompatible from int[]. Type promotion does not work for arrays."); - } - } - - private static void uncheckedConversion() { - Box originalBox = new Box<>(); - Box raw = originalBox; - raw.setContent(2.5); - Box bound = (Box) raw; - try { - Long content = bound.getContent(); - } catch (ClassCastException e) { - System.out.println("An incompatible element was found in the raw box."); - } - } - - private static void genericConversion() { - try { - String shouldBeNull = convertInstanceOfObject(123); - } catch (ClassCastException e) { - System.out.println("Should have been null, but due to type erasure, inside convertInstanceOfObject, " + - "it will attempt to cast to Object instead of String, so it casts to Object, which is always possible."); - } - } - - public static T convertInstanceOfObject(Object o) { - try { - return (T) o; - } catch (ClassCastException e) { - return null; - } - } - - public interface Animal { - } - - public static class Reptile implements Animal { - } - - public static class Frog extends Reptile { - } - - public static class Mammal implements Animal { - } - - public static class Box { - private T content; - - public T getContent() { - return content; - } - - public void setContent(T content) { - this.content = content; - } - } - -} diff --git a/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Mammal.java b/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Mammal.java new file mode 100644 index 0000000000..2723cc5b7b --- /dev/null +++ b/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Mammal.java @@ -0,0 +1,9 @@ +package com.baeldung.exceptions.classcastexception; + +public class Mammal implements Animal { + + @Override + public String getName() { + return "Mammal"; + } +} diff --git a/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Reptile.java b/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Reptile.java new file mode 100644 index 0000000000..ed4b0273e5 --- /dev/null +++ b/core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Reptile.java @@ -0,0 +1,9 @@ +package com.baeldung.exceptions.classcastexception; + +public class Reptile implements Animal { + + @Override + public String getName() { + return "Reptile"; + } +} diff --git a/core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/CheckedCastsUnitTest.java b/core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/CheckedCastsUnitTest.java new file mode 100644 index 0000000000..7fac000fa8 --- /dev/null +++ b/core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/CheckedCastsUnitTest.java @@ -0,0 +1,40 @@ +package com.baeldung.exceptions.classcastexception; + +import org.junit.Test; + +import java.io.Serializable; + +public class CheckedCastsUnitTest { + + @Test(expected = ClassCastException.class) + public void givenBaseTypeVariableReferencingChildInstance_whenCastToIncompatibleSubtype_thenClassCastException() { + Animal animal = new Frog(); + + //A checked downcast to Mammal is incompatible from Frog because Frog is not a subtype of Mammal. + Mammal mammal = (Mammal) animal; + } + + @Test(expected = ClassCastException.class) + public void givenBaseTypeVariableReferencingChildInstance_whenCastToIncompatibleInterface_thenClassCastException() { + Animal animal = new Frog(); + + //A checked cast to Serializable is incompatible from Frog because Frog is not a subtype of Serializable. + Serializable serial = (Serializable) animal; + } + + @Test(expected = ClassCastException.class) + public void givenObjectVariableReferencingPrimitiveArray_whenCastToBoxedTypeArray_thenClassCastException() { + Object primitives = new int[1]; + + //A checked cast to Integer[] is incompatible from primitive arrays. Auto-boxing does not work for arrays. + Integer[] integers = (Integer[]) primitives; + } + + @Test(expected = ClassCastException.class) + public void givenObjectVariableReferencingPrimitiveArray_whenCastToPromotedTypeArray_thenClassCastException() { + Object primitives = new int[1]; + + //A checked cast to long[] is incompatible from int[]. Type promotion does not work for arrays. + long[] longs = (long[]) primitives; + } +} diff --git a/core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/GenericConversionUnitTest.java b/core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/GenericConversionUnitTest.java new file mode 100644 index 0000000000..027ece2db7 --- /dev/null +++ b/core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/GenericConversionUnitTest.java @@ -0,0 +1,21 @@ +package com.baeldung.exceptions.classcastexception; + +import org.junit.Test; + +public class GenericConversionUnitTest { + + @Test(expected = ClassCastException.class) + public void givenIncompatibleType_whenConvertInstanceOfObject_thenClassCastException() { + // Should have been null, but due to type erasure, inside convertInstanceOfObject, + // it will attempt to cast to Object instead of String, so it casts to Object, which is always possible. + String shouldBeNull = convertInstanceOfObject(123); + } + + public static T convertInstanceOfObject(Object o) { + try { + return (T) o; // Casts to Object due to type erasure + } catch (ClassCastException e) { + return null; // Will never reach this + } + } +} diff --git a/core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/UncheckedConversionUnitTest.java b/core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/UncheckedConversionUnitTest.java new file mode 100644 index 0000000000..60e7d5a147 --- /dev/null +++ b/core-java-modules/core-java-exceptions-3/src/test/java/com/baeldung/exceptions/classcastexception/UncheckedConversionUnitTest.java @@ -0,0 +1,17 @@ +package com.baeldung.exceptions.classcastexception; + +import org.junit.Test; + +public class UncheckedConversionUnitTest { + + @Test(expected = ClassCastException.class) + public void givenPollutedGenericType_whenGetProperty_thenClassCastException() { + Box originalBox = new Box<>(); + Box raw = originalBox; + raw.setContent(2.5); + Box bound = (Box) raw; + + //An incompatible element was found in the raw box. + Long content = bound.getContent(); + } +}