Explanation of “ClassCastException” in Java

core-java-modules/core-java-exceptions-3/src/main/java/com/baeldung/exceptions/classcastexception/Main.java

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+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<Long> originalBox = new Box<>();
+        Box raw = originalBox;
+        raw.setContent(2.5);
+        Box<Long> bound = (Box<Long>) 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> 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<T> {
+        private T content;
+
+        public T getContent() {
+            return content;
+        }
+
+        public void setContent(T content) {
+            this.content = content;
+        }
+    }
+}