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Understanding Java Exceptions vs RuntimeExceptions

Table of Contents

Java exceptions and runtime exceptions are key concepts for handling errors and exceptional cases in your code. But when should you use each one. This comprehensive guide will teach you the differences, uses, and best practices so you can write more robust and resilient Java applications.

At a Glance

Here are the key differences between exceptions and runtime exceptions:

  • Checked exceptions (subclasses of Exception) must be caught or declared. The compiler enforces handling.
  • Runtime exceptions (subclasses of RuntimeException) don’t need to be explicitly handled.
  • Use checked exceptions for recoverable conditions like IO issues.
  • Use runtime exceptions for programming errors like divide by zero.
  • Overuse of runtime exceptions can hurt debugging. Reserve for unrecoverable cases.

Defining Checked Exceptions

Checked exceptions are subclasses of the Exception class in Java. They represent invalid conditions in areas outside the immediate control of the program like:

  • Hardware faults
  • Network outages
  • Invalid user input
  • Accessing files that don’t exist
  • API call failures

These exceptions are called “checked” because the compiler checks that they are handled in some way. If a method might throw a checked exception, it must either:

  • Catch it using try-catch blocks
  • Declare it in the method signature using throws

Here’s an example of a checked exception for a missing file:

try {
  File myFile = new File("data.txt");
  FileReader fr = new FileReader(myFile); 
} catch (FileNotFoundException e) {
  // Handle missing file
}

This forces the developer to anticipate the issue and handle it appropriately.

Understanding Runtime Exceptions

Runtime exceptions are subclasses of RuntimeException. They generally indicate programming errors made by the developer like:

  • Null pointer dereferencing
  • Array index out of bounds
  • Dividing by zero

Runtime exceptions are known as “unchecked” because the compiler doesn’t enforce handling them. The code will compile even with the potential for a runtime exception.

For example:

int x = 5;
int y = 0; 
int z = x / y; // Throws ArithmeticException

Since these are considered programming errors, runtime exceptions may be left unhandled. But this can lead to unexpected crashes in production.

Key Differences

Checked ExceptionsRuntime Exceptions
Used for recoverable external errorsUsed for programming errors
Must be caught or declaredCan be left unhandled
Checked by the compilerUnchecked by the compiler
Ex: FileNotFoundExceptionEx: NullPointerException

When to Use Each One

Use checked exceptions for cases where you want to force handling the error, especially for recoverable cases. This includes:

  • Hardware or system failures
  • Network issues
  • Reading/writing files
  • Invalid user input

Use runtime exceptions for programming errors or special cases where recovery may not be possible, like:

  • Accessing null objects
  • Out of bounds errors
  • Dividing by zero

However, avoid overusing runtime exceptions when checked exceptions would be more appropriate. For example, throwing a RuntimeException for a missing file is usually not advisable.

Benefits of Proper Exception Handling

  • Prevents crashes – Handling exceptions prevents abrupt halts and provides resilience.
  • Centralized handling – Grouped handling in one place reduces duplication.
  • Cleaner code – Less clutter from try-catch blocks scattered throughout.
  • Improved debugging – Tracing is easier with handled exceptions pointing to sources.
  • Better documentation – Declared exceptions document expected errors.
  • More readable code – Explicitly handled exceptions make logic flow clear.

Best Practices

Follow these best practices when leveraging exceptions:

  • Use checked exceptions for recoverable cases and force handling.
  • Reserve runtime exceptions for programming errors and unrecoverable events.
  • Avoid overuse of runtime exceptions.
  • Document exceptions thrown with Javadoc comments.
  • Catch exceptions at an appropriate level – avoid too broad catching.
  • Log caught exceptions for debugging and include messages/context.
  • Allow execution to continue after handling exceptions where possible.
  • Rethrow exceptions or wrap in custom exceptions if needed.

Conclusion

Understanding the differences between checked exceptions and runtime exceptions is crucial for writing solid Java code. Use checked exceptions to make your software resilient to real world errors. Use runtime exceptions for coding errors and special cases.

Anand Das

Anand Das

Anand is Co-founder and CTO of Bito. He leads technical strategy and engineering, and is our biggest user! Formerly, Anand was CTO of Eyeota, a data company acquired by Dun & Bradstreet. He is co-founder of PubMatic, where he led the building of an ad exchange system that handles over 1 Trillion bids per day.

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