Java ClassCastException

Introduction

ClassCastException in Java is a runtime exception that occurs when an object is cast to a class of which it is not an instance. This helps identify type mismatch errors in your code.

Table of Contents

1. What is ClassCastException?
2. Common Causes
3. Handling ClassCastException
4. Examples of ClassCastException
5. Conclusion

1. What is ClassCastException?

ClassCastException is thrown when an object is forcibly cast to a class it does not belong to, indicating a type mismatch.

2. Common Causes

• Incorrect casting between unrelated classes.
• Casting without proper checks using instanceof.

3. Handling ClassCastException

To handle ClassCastException, use a try-catch block and ensure proper type checking with instanceof before casting.

4. Examples of ClassCastException

Example 1: Incorrect Casting

This example demonstrates handling a ClassCastException when casting an object to an incompatible type.

public class IncorrectCastingExample { public static void main(String[] args) { Object obj = "Hello"; try { Integer num = (Integer) obj; // Incorrect casting } catch (ClassCastException e) { System.out.println("Error: Cannot cast String to Integer."); } } } 

Output:

Error: Cannot cast String to Integer. 

Example 2: Safe Casting with instanceof

This example shows how to safely cast an object using instanceof to avoid ClassCastException.

public class SafeCastingExample { public static void main(String[] args) { Object obj = "Hello"; if (obj instanceof String) { String str = (String) obj; // Safe casting System.out.println("String value: " + str); } else { System.out.println("Object is not a String."); } } } 

Output:

String value: Hello 

Conclusion

ClassCastException is an important mechanism in Java for identifying type mismatch errors during casting. By properly handling this exception and using type checks, you can ensure type safety in your applications, leading to more robust and reliable code.