Java Exceptions

Java Exceptions

1. Checked Exceptions: These are exceptions that are checked at compile time. Any method that might throw a checked exception must declare it in the throws clause of its method signature, or handle it using a try-catch block.

 import java.io.*;

public class CheckedExceptionExample {
    public static void main(String[] args) {
        try {
            BufferedReader reader = new BufferedReader(new FileReader("file.txt"));
            String line = reader.readLine();
            System.out.println("First line of file: " + line);
            reader.close();
        } catch (IOException e) {
            System.out.println("An error occurred while reading the file: " + e.getMessage());
        }
    }
}
      

2. Unchecked Exceptions (Runtime Exceptions): These are exceptions that are not checked at compile time. They typically represent programming errors or unexpected conditions and extend RuntimeException or its subclasses.

        public class UncheckedExceptionExample {
            public static void main(String[] args) {
                try {
                    int result = 10 / 0; // ArithmeticException: divide by zero
                } catch (ArithmeticException e) {
                    System.out.println("An arithmetic error occurred: " + e.getMessage());
                }
            }
        }
      

3. Custom Exceptions: You can define your own exception classes by extending Exception or one of its subclasses.

        public class CustomExceptionExample {
            static void validateAge(int age) throws InvalidAgeException {
                if (age < 18) {
                    throw new InvalidAgeException("Age must be at least 18");
                } else {
                    System.out.println("Age is valid");
                }
            }
        
            public static void main(String[] args) {
                try {
                    validateAge(15);
                } catch (InvalidAgeException e) {
                    System.out.println("An error occurred: " + e.getMessage());
                }
            }
        }
        
        class InvalidAgeException extends Exception {
            public InvalidAgeException(String message) {
                super(message);
            }
        }
      

4. Finally Block: The finally block is used to execute code that should always be run, regardless of whether an exception is thrown or not.

        public class FinallyBlockExample {
            public static void main(String[] args) {
                try {
                    System.out.println("Try block");
                    int result = 10 / 0;
                } catch (ArithmeticException e) {
                    System.out.println("Catch block");
                } finally {
                    System.out.println("Finally block");
                }
            }
        }