Exceptions in Java are events that disrupt the normal flow of a program's execution. They are used to handle errors and other exceptional events that may occur during runtime.

Types of Exceptions

  1. Checked Exceptions (compile-time exceptions)

    • Must be declared or handled (using try-catch or throws)
    • Examples: IOException, SQLException, ClassNotFoundException

  2. Unchecked Exceptions (runtime exceptions)

    • Not checked at compile time
    • Examples: NullPointerException, ArrayIndexOutOfBoundsException, ArithmeticException

  3. Errors

    • Serious problems that applications should not try to catch
    • Examples: OutOfMemoryError, StackOverflowError

Exception Handling Keywords

  • try: Block of code to monitor for exceptions
  • catch: Block that handles the exception
  • finally: Block that always executes (for cleanup)
  • throw: Used to explicitly throw an exception
  • throws: Declares exceptions that might be thrown by a method

Example 

try {
    // Code that might throw an exception
    int result = 10 / 0; // This will throw ArithmeticException
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero!");
} catch (Exception e) {
    System.out.println("General exception caught");
} finally {
    System.out.println("This will always execute");
}

Custom Exceptions

You can create your own exception classes by extending Exception (checked) or RuntimeException (unchecked):

class MyCustomException extends Exception {
    public MyCustomException(String message) {
        super(message);
    }
}

Best Practices

  1. Catch specific exceptions rather than general Exception
  2. Don't ignore caught exceptions (empty catch blocks)
  3. Use finally blocks for resource cleanup
  4. Document exceptions with @throws in JavaDoc
  5. Consider whether to handle, propagate, or convert exceptions

Would you like more details on any specific aspect of Java exceptions?