Creating custom exception class in Java - Quick Revision & Summary

Recall & Review

beginner

What is a custom exception class in Java?

A custom exception class is a user-defined class that extends the Exception class (or one of its subclasses) to create specific error types for your program.

beginner

How do you declare a custom checked exception in Java?

You create a class that extends Exception and provide constructors, usually calling super() to pass messages or causes.

beginner

Why would you create a custom exception class?

To represent specific error conditions in your program clearly, making error handling easier and your code more readable.

intermediate

What is the difference between checked and unchecked exceptions in Java?

Checked exceptions must be declared or handled; they extend Exception. Unchecked exceptions extend RuntimeException and don't require explicit handling.

beginner

Show a simple example of a custom exception class in Java.

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

Which class should you extend to create a checked custom exception in Java?

A Error

B Exception

C RuntimeException

D Throwable

Checked exceptions extend Exception but not RuntimeException.

What keyword is used to throw a custom exception in Java?

A throws

B catch

C throw

D try

The 'throw' keyword is used to actually throw an exception object.

Which constructor is commonly called inside a custom exception class constructor?

A super()

B this()

C new Exception()

D parent()

super() calls the parent Exception class constructor.

If you want an exception that does NOT require explicit handling, which class should you extend?

A RuntimeException

B Exception

C Error

D Throwable

RuntimeException and its subclasses are unchecked exceptions.

What is the purpose of creating a custom exception?

A To replace all built-in exceptions

B To avoid using try-catch blocks

C To speed up program execution

D To represent specific error conditions clearly

Custom exceptions help make error handling clearer and more specific.

Explain how to create a custom checked exception class in Java and why you might need one.

Think about extending Exception and passing messages.

Describe the difference between checked and unchecked exceptions and how this affects creating custom exceptions.

Focus on exception hierarchy and handling requirements.