Inno 3.5 Exceptions Flashcards
(17 cards)
Q: What is the difference between Exception, ApplicationException, and SystemException in .NET?
Exception: The base class for all exceptions in .NET. All exception types ultimately inherit from this class, including system-level exceptions, application exceptions, and custom exceptions.
ApplicationException: A derived class from Exception that was originally intended to be used as a base class for exceptions specific to application logic. However, in practice, it’s seldom used because the general Exception class can serve the same purpose.
SystemException: Another derived class from Exception, but it represents exceptions that are system-related, such as NullReferenceException and InvalidOperationException. These exceptions usually arise from system-level issues, such as memory access violations or invalid operations.
Q: What is NullReferenceException, and why does it occur?
A NullReferenceException occurs when an application attempts to access a method or property on an object reference that is null. For example, if you have an object but forget to initialize it, calling any member of that object will trigger this exception.
Why it occurs: This is a runtime exception and happens because .NET doesn’t automatically check for null references in most situations.
How to prevent: To avoid this exception, you can use null checks (if (obj != null)), nullable value types, or the null-conditional operator (?.) introduced in C# 6.
Q: How does InvalidOperationException differ from ArgumentException in .NET?
InvalidOperationException: This exception is thrown when a method call is not valid for the current state of the object. It’s typically used when an operation cannot be performed due to the object being in an invalid state, even though the arguments passed may be correct.
Example: Calling MoveNext on an enumerator after it has already iterated through all elements.
ArgumentException: This exception is thrown when a method receives an argument that is not valid for the expected input. It’s typically used when the problem lies with the arguments passed to a method, such as an invalid parameter.
Example: Passing a negative value for an argument that expects a positive number.
Q: Why is it important to create custom exceptions in your .NET application?
Creating custom exceptions provides several benefits:
Semantic Clarity: Custom exceptions can give a clear meaning to specific error scenarios, making it easier for developers to understand what went wrong and where. For example, creating an exception like PaymentProcessingException can tell you that the issue is specifically related to payment processing. Better Error Handling: By defining custom exceptions, you can handle specific error cases more gracefully. It allows catching specific exception types and applying tailored error handling logic, rather than handling all errors with a general Exception. Extendable: Custom exceptions can be extended to include additional properties, such as error codes or additional context, making them more informative than the generic Exception class.
Q: How does try-catch-finally work in exception handling in .NET?
try: This block contains the code that may throw an exception. If an exception is thrown, control moves to the catch block.
catch: This block handles exceptions thrown in the try block. You can specify the type of exception to catch (e.g., InvalidOperationException) or use a generic Exception to catch all exceptions. You can also have multiple catch blocks to handle different types of exceptions differently.
finally: This block always executes after the try-catch blocks, regardless of whether an exception was thrown or not. It’s commonly used to clean up resources, such as closing file streams or database connections.
Q: What is the role of the finally block in exception handling?
The finally block is used to ensure that certain **clean-up code **runs, regardless of whether an exception was thrown or not. It is executed after the try block (and any catch blocks) complete execution, making it ideal for resource management tasks like:
Closing file handles, database connections, or network resources.
Releasing unmanaged resources (like memory or hardware devices).
Even if an exception is thrown or a return statement is executed in the try block, the finally block will still be executed.
Q: What’s the difference between throw and throw ex in .NET?
throw: When used without an object, throw rethrows the current exception while preserving the original stack trace. This is useful when you want to catch an exception, log it, and then propagate it upwards in the call stack.
throw ex: When an exception is explicitly rethrown using throw ex, the stack trace is lost, and the exception appears as though it was thrown for the first time in the location of the rethrow. This is generally discouraged because it can obscure the original cause of the exception.
Q: How does exception handling work in async code, and what is an AggregateException?
In async code, exceptions can be captured and stored in a Task object. When an exception occurs in an async method, it is wrapped in an AggregateException if the exception is thrown while the Task is running.
The aggregate exception can be accessed via the Task.Exception property.
Task.Exception: This property contains an AggregateException that holds one or more inner exceptions. To access individual exceptions, you can loop through the InnerExceptions collection of the AggregateException.
Q: What’s the difference between a normal exception and an exception in async code?
Normal Exceptions: In synchronous code, exceptions are thrown immediately when the problem occurs and can be caught using try-catch blocks.
Async Exceptions: In async code, exceptions are not thrown until the Task is awaited. If an exception occurs in an asynchronous method, it is not thrown directly but instead captured by the Task and can be caught later when the task is awaited or when its result is accessed. This behavior leads to the use of AggregateException.
Q: How does the Exception Handling Mechanism in .NET differ from other programming languages like Java or Python?
In .NET, exceptions are objects derived from the Exception class. When an exception occurs, a new exception object is created, and control is transferred to the catch block. In .NET, try-catch-finally blocks are used to handle exceptions, similar to Java.
Java has checked exceptions, meaning the compiler forces you to handle certain exceptions explicitly, while .NET only has unchecked exceptions (i.e., all exceptions inherit from System.Exception, and the compiler doesn’t require explicit handling).
In Python, exceptions are also objects, but Python uses a more lenient exception model, where the developer doesn’t need to specify what exceptions a method can throw. Python encourages handling specific exceptions to minimize unnecessary broad exception handling.
Q: When is it appropriate to throw an exception manually in .NET, and what are the best practices for doing so?
You should throw an exception in scenarios where the current method cannot continue its execution due to an unexpected condition, like invalid input or an unexpected state. Some best practices include:
Use descriptive exception types: Throw an exception that accurately describes the error, such as ArgumentException for invalid parameters or InvalidOperationException when a method cannot execute in the current state. Don’t throw generic exceptions: Throw specific exceptions, such as FileNotFoundException or TimeoutException, instead of just throwing Exception. Document the exceptions: Use comments or documentation to specify the conditions under which the exceptions might be thrown. Ensure proper exception handling: Always ensure that any thrown exceptions are properly caught and handled in higher layers, or log them appropriately for troubleshooting.
Q: How can you improve the reusability and clarity of custom exceptions in .NET?
To make custom exceptions more reusable and clear:
Provide meaningful names: Name custom exceptions according to the type of error they represent. For example, DatabaseConnectionFailedException or InsufficientFundsException are much clearer than generic names. Add custom properties: Allow exceptions to carry more information, such as ErrorCode, Timestamp, or other relevant data. This helps consumers of the exception gain more context when it is caught. Ensure your custom exceptions are serializable: Use the [Serializable] attribute to allow exceptions to be serialized when needed, especially for distributed applications or logging. Inherit from appropriate base types: Derive your custom exceptions from more specific types, such as ApplicationException or InvalidOperationException, rather than directly from Exception, to provide clearer context.
Q: What is the propagation of exceptions in the call stack, and how does it work in .NET?
Exception propagation in .NET works by unwinding the call stack:
When an exception is thrown, the runtime searches for a catch block in the current method. If none is found, it looks in the calling method, and continues to search upward through the call stack until a handler is found. If no handler is found by the time the top-level method (e.g., Main() in a console app) is reached, the UnhandledException event is triggered, and the application typically terminates. Rethrowing exceptions: If an exception is caught but needs to be passed to higher layers, you can rethrow it using throw (without specifying the exception), which preserves the original stack trace. If you use throw ex, the stack trace will be lost, and the exception appears to be thrown from the rethrow point.
Q: How does Async/Await affect exception handling, and how do exceptions behave when using async code in .NET?
In async methods, exceptions are not thrown immediately when they occur but are captured and wrapped inside the Task object. When you await the task, the exception is rethrown, allowing it to be caught using standard try-catch blocks.
AggregateException: If multiple exceptions are thrown during asynchronous operations, they are wrapped in an AggregateException and can be accessed via the Task.Exception property. This is common when you use methods like Task.WhenAll() or Task.WhenAny().
Q: How does the Task.Exception property work in asynchronous code, and when should it be used?
The Task.Exception property is used to retrieve exceptions that occurred during the execution of an asynchronous task.
This property holds an AggregateException if one or more exceptions were thrown during task execution. Each inner exception can be accessed using the InnerExceptions collection of the AggregateException.
You typically access Task.Exception when the task has completed in a failed state, and you want to examine or handle the error after the task has finished.
Q: When should you not catch exceptions in your .NET code?
Don’t catch exceptions just to suppress them: Catching exceptions without properly handling them (e.g., just logging or ignoring them) can hide underlying issues and lead to harder-to-debug problems.
Avoid catching generic exceptions: Catching Exception should be reserved for scenarios where it’s necessary to catch any exception, such as in a top-level exception handler. It’s better to catch specific exceptions to avoid catching unexpected ones.
Don’t catch exceptions that are already handled by the system: For instance, NullReferenceException and InvalidOperationException should generally be avoided unless you need to handle specific application logic. Let the runtime handle these errors when they’re predictable.
