Mostly Asked Java Exception Handling Questions

Q1. What is exception handling in Java?What is exception handling in Java?

Exception handling is a mechanism to handle runtime errors, allowing the normal flow of the program to continue. It uses try, catch, finally blocks to catch exceptions and handle them gracefully.

try {
  int result = 10 / 0;
} catch (ArithmeticException e) {
  System.out.println("Cannot divide by zero.");
} finally {
  System.out.println("Execution completed.");
}

Q2. Difference between checked and unchecked exceptions?Difference between checked and unchecked exceptions?

Checked exceptions are checked at compile time and must be handled using try-catch or declared with throws. Examples: IOException, SQLException.
Unchecked exceptions occur at runtime and don't need mandatory handling. Examples: NullPointerException, ArithmeticException.

Q3. What is the purpose of finally block?What is the purpose of finally block?

The finally block always executes after try and catch blocks, regardless of exception occurrence. It is used to release resources like closing files, database connections.

Q4. How to create a custom exception in Java?How to create a custom exception in Java?

Create a class extending Exception or RuntimeException and provide constructors. You can throw instances of this class to represent application-specific errors.

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

Q5. What is the difference between throw and throws?What is the difference between throw and throws?

throw is used to explicitly throw an exception from a method or block.
throws is used in method signature to declare exceptions that might be thrown.

void checkAge(int age) throws IllegalArgumentException {
  if (age < 18) {
    throw new IllegalArgumentException("Age must be 18 or older.");
  }
}

Q6. Can multiple catch blocks be used? Explain.Can multiple catch blocks be used? Explain.

Yes, multiple catch blocks can handle different types of exceptions separately. Java checks the catch blocks from top to bottom and executes the first matching one.

try {
  int[] arr = new int[5];
  System.out.println(arr[10]);
} catch (ArrayIndexOutOfBoundsException e) {
  System.out.println("Array index is out of bounds.");
} catch (Exception e) {
  System.out.println("General exception caught.");
}

Q7. What is the use of try-with-resources statement?What is the use of try-with-resources statement?

Try-with-resources automatically closes resources like streams or files after use, eliminating the need for explicit finally blocks to close them.

try (BufferedReader br = new BufferedReader(new FileReader("file.txt"))) {
  String line;
  while ((line = br.readLine()) != null) {
    System.out.println(line);
  }
} catch (IOException e) {
  e.printStackTrace();
}

Q8. What is the difference between Error and Exception?What is the difference between Error and Exception?

Errors are serious problems that applications should not catch (e.g., OutOfMemoryError). Exceptions are conditions that applications might want to catch and handle.

Q9. Explain the hierarchy of exception classes in Java.Explain the hierarchy of exception classes in Java.

Throwable is the superclass of all errors and exceptions.
- Error: Serious problems, not meant to be caught.
- Exception: Can be checked or unchecked.
-- Checked exceptions must be declared or caught.
-- Runtime exceptions (unchecked) need not be declared or caught.

Q10. How do you handle multiple exceptions in one catch block?How do you handle multiple exceptions in one catch block?

Since Java 7, multiple exceptions can be caught in a single catch block using pipe '|' operator.

try {
  // code
} catch (IOException | SQLException ex) {
  ex.printStackTrace();
}