Throwing custom exceptions in Java - Cheat Sheet & Quick Revision

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beginner

What is a custom exception in Java?

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

beginner

How do you define a custom checked exception?

Create a class that extends Exception and provide constructors to pass error messages or causes.

beginner

How do you throw a custom exception in Java?

Use the throw keyword followed by an instance of your custom exception, e.g., throw new MyException("Error message");

intermediate

What is the difference between checked and unchecked custom exceptions?

Checked exceptions extend Exception and must be declared or handled. Unchecked exceptions extend RuntimeException and do not require explicit handling.

intermediate

Why create custom exceptions instead of using standard exceptions?

Custom exceptions make your code clearer by signaling specific problems related to your application logic, improving error handling and debugging.

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

A throw

B throws

C catch

D try

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

To create a checked custom exception, your class should extend which class?

A RuntimeException

B Error

C Throwable

D Exception

Checked exceptions extend Exception but not RuntimeException.

What must you do when a method throws a checked custom exception?

A Declare it with throws or handle it with try-catch

B Ignore it

C Only declare it with throws, no handling needed

D Use finally block only

Checked exceptions require declaration or handling.

Which of these is NOT a reason to create a custom exception?

A To make error messages more specific

B To handle errors related to your application logic

C To replace all standard exceptions

D To improve debugging

Custom exceptions complement, not replace, standard exceptions.

Which class should a custom unchecked exception extend?

A Exception

B RuntimeException

C Error

D Throwable

Unchecked exceptions extend RuntimeException.

Explain how to create and throw a custom checked exception in Java.

Think about class inheritance and method declaration.

Why is it useful to create custom exceptions instead of using only built-in exceptions?

Consider how specific error types help programmers.