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9 Kotlin errors you should know: A comprehensive debugging guide for Kotlin exceptions

Bhargava MNN
~ 5 min read | Published on Feb 28, 2024


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Error handling is an essential part of software development, ensuring that your code runs smoothly and handles unexpected issues gracefully. In Kotlin, errors are represented as exceptions, which are raised when abnormal conditions occur during program execution. It's crucial to understand and effectively handle Kotlin errors to create robust and reliable applications.

But do you know the most common Kotlin errors and how to tackle them? Are you familiar with the different types of Kotlin exceptions that developers often encounter? In this comprehensive debugging guide, we'll explore nine Kotlin errors that you should be aware of. From NullPointerExceptions to ArrayIndexOutOfBoundsExceptions, we'll dive into the causes, strategies for handling, and tips for preventing these errors in your Kotlin code.

Get ready to level up your error-handling skills and make your Kotlin code more resilient. Let's unravel the mysteries of Kotlin errors together!

Key Takeaways:

  • Understanding Kotlin errors is vital for creating robust applications.
  • Kotlin exceptions are raised when abnormal conditions occur during program execution.
  • In this guide, we'll explore nine common Kotlin errors and how to handle them.
  • Learn about NullPointerExceptions, ArrayIndexOutOfBoundsExceptions, ClassCastExceptions, NumberFormatExceptions, IllegalArgumentExceptions, IllegalStateExceptions, OutOfMemoryErrors, SecurityExceptions, and NetworkOnMainThreadExceptions.
  • Discover best practices for effective error handling in Kotlin.

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1. Kotlin NullPointerException

The Kotlin NullPointerException (also known as null reference exception) is a common Kotlin error encountered by developers when working with Kotlin. This type of Kotlin error occurs when a null reference is accessed or used in a way that requires a non-null value. Handling Kotlin errors, particularly null exceptions, is crucial to ensure the stability and reliability of your code.

There are several causes of Kotlin errors like NullPointerException in Kotlin. One common cause of this Kotlin error is attempting to access a variable or object that has not been initialized or assigned a value. Another cause of Kotlin errors is passing a null argument to a method or function that expects a non-null value. It is important to be aware of these possible causes of Kotlin errors and take appropriate steps to prevent null references.

When it comes to handling null exceptions, Kotlin provides several strategies that can be used to avoid Kotlin errors. One approach to prevent Kotlin errors is to use the safe call operator (?), which allows you to safely access properties or call methods on nullable objects without throwing NullPointerException, a frequent Kotlin error. Another approach to mitigate Kotlin errors is to use the Elvis operator (?:) to provide a default value when a nullable object is null. Additionally, Kotlin provides the option to use the safe cast operator (as?) to safely cast objects and avoid ClassCastException, another type of Kotlin error.

To prevent Kotlin errors like NullPointerExceptions, it is good practice to always initialize variables and objects before they are used, especially if they are expected to have non-null values. You can also use the 'lateinint' modifier to declare properties that will be assigned a value later in the code, thus avoiding Kotlin errors. Another effective approach is to use Kotlin's type system features, such as nullable types and non-null assertions, to enforce null safety at compile-time and reduce the occurrence of Kotlin errors.

Code examples to understand how to handle Kotlin NullPointerException >>

By understanding the causes of NullPointerException, applying appropriate strategies for handling null exceptions, and adopting preventive measures, you can effectively manage null references and ensure the robustness and reliability of your Kotlin code.

2. Kotlin ArrayIndexOutOfBoundsException

In Kotlin, the ArrayIndexOutOfBoundsException is raised when an invalid or out-of-range index is used to access an array element. This exception occurs when the index provided is either negative or exceeds the size of the array.

To handle the ArrayIndexOutOfBoundsException in Kotlin, you can use try-catch blocks to catch the exception and provide appropriate error handling code. Within the catch block, you can log the error, display a user-friendly message, or take any necessary actions to handle the exceptional case. By gracefully handling this exception, you can prevent your program from crashing and provide a better user experience.

Code examples to understand how to handle Kotlin ArrayIndexOutOfBoundsException >>

When working with arrays, it is important to ensure that your code does not access array elements using invalid or out-of-range indices. This can be achieved by validating the index before attempting to access the array element. You can use conditional statements such as if statements to check if the index is within the valid range of indices for the array. By implementing such validation checks, you can avoid encountering ArrayIndexOutOfBoundsException errors.

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3. Kotlin ClassCastException

The Kotlin ClassCastException is a common error that occurs when an object is cast to a type that is not compatible with its actual type. This can happen when there is a misunderstanding of the type hierarchy or when incompatible types are used in a polymorphic context.

To handle the ClassCastException in Kotlin, it is important to carefully consider the types involved and ensure that the casting operation is valid. Here are some strategies to handle this exception effectively:

  1. Use the 'as?' keyword: Instead of using the regular 'as' operator for casting, prefer the 'as?' operator, which returns null if the casting is not possible.
  2. Avoid unnecessary casts: Before performing a cast, consider checking the type with the 'is' operator to avoid unnecessary casting and potential ClassCastException.
  3. Implement error handling: Wrap your casting operations with a try-catch block to catch the ClassCastException and handle it gracefully. This allows you to perform alternative actions or provide appropriate error messaging.
  4. Follow best practices: To minimize the occurrence of ClassCastException, it is essential to design your codebase with clear and consistent type hierarchies, adhere to proper object-oriented programming principles, and utilize Kotlin's powerful type system effectively.

Code examples to understand how to handle Kotlin ClassCastException >>

By following these strategies, you can effectively handle ClassCastException in your Kotlin code and improve the overall stability and reliability of your applications.



Misunderstanding of type hierarchy

Ensure a clear understanding of the type hierarchy and validate the compatibility of types before performing casts.

Incompatible types in a polymorphic context

Use the 'as?' operator and perform safe casting or follow proper type-checking techniques to avoid incompatible type situations.


4. Kotlin NumberFormatException

The Kotlin NumberFormatException is a specific type of exception that occurs when a string cannot be converted into a numeric value of the expected type. This exception is thrown when there is an error in the number formatting, such as an invalid character or an incompatible format.

There are several common causes for the NumberFormatException in Kotlin:

  1. Attempting to parse a non-numeric string into a numeric value
  2. Using a decimal separator that is not recognized by the current locale
  3. Using a format specifier that is incompatible with the target numeric type

To handle the NumberFormatException in Kotlin, you can use the try-catch block to catch the exception and perform appropriate error handling. Here's an example:

try { val number = string.toDouble() // Perform further operations on the parsed number } catch (e: NumberFormatException) { // Handle the exception, display an error message, or perform any other necessary actions }

When handling the NumberFormatException, it's important to provide meaningful and user-friendly error messages to help users understand the issue and take appropriate actions.

To avoid number formatting errors and prevent the occurrence of NumberFormatException, you can follow these tips:

  • Validate user input to ensure it conforms to the expected numeric format before parsing.
  • Use the appropriate number formatting functions/classes in Kotlin, such as toDouble() or toInt(), depending on the desired type.
  • Consider using number formatting libraries or utility functions that can handle different number formats and locales more robustly.
  • Test your code thoroughly by providing different input values to ensure it can handle a variety of scenarios.

Code examples to understand how to handle Kotlin NumberFormatException >>

By following these strategies for handling the Kotlin NumberFormatException and taking preventive measures, you can write more reliable and robust Kotlin code that gracefully handles number formatting errors.


Handling Strategy

Attempting to parse a non-numeric string into a numeric value

Validate user input before parsing, and handle the exception using the try-catch block.

Using a decimal separator that is not recognized by the current locale

Use the appropriate number formatting functions/classes in Kotlin that handle different locales, or validate and normalize the decimal separator.

Using a format specifier that is incompatible with the target numeric type

Ensure that the format specifier matches the desired numeric type and handle the exception using the try-catch block.


5. Kotlin IllegalArgumentException

The Kotlin IllegalArgumentException is a type of Kotlin error that occurs when an invalid or inappropriate argument is passed to a method or function in Kotlin. This Kotlin error can occur when the argument does not meet the expected conditions or requirements for the operation being performed.

There are several potential causes for Kotlin errors like the IllegalArgumentException in Kotlin:

  1. An argument is null when a non-null value is required, a common Kotlin error.
  2. An argument falls outside the valid range of values, leading to Kotlin errors.
  3. An argument does not match the expected data type, resulting in Kotlin errors.
  4. An argument violates a specific constraint or condition set by the method or function, causing Kotlin errors.

To handle the IllegalArgumentException effectively in Kotlin and prevent such Kotlin errors, you can employ the following techniques:

  • Use try-catch blocks to catch and handle this kind of Kotlin error. This allows you to gracefully respond to the invalid argument without causing application crashes or unexpected behavior.
  • Implement input validation to check the validity of arguments before using them. This can include checking for null values, verifying if the argument falls within the expected range, or confirming that the argument matches the required data type, thus preventing Kotlin errors.
  • Provide clear and informative error messages that indicate the specific issue with the argument. This helps developers understand why the Kotlin error occurred and how to resolve it.
  • Utilize proper documentation and specifications for methods and functions to communicate the expected arguments and their constraints. This can prevent developers from passing inappropriate or invalid arguments in the first place, thereby reducing the likelihood of such Kotlin errors.

Code examples to understand how to handle Kotlin IllegalArgumentException >>

By following these techniques, you can handle and prevent illegal argument errors in your Kotlin code, promoting robustness and reliability in your applications.

6. Kotlin IllegalStateException

The Kotlin IllegalStateException is a runtime exception that occurs when the state of an object is not suitable for the requested operation. This exception is thrown to indicate that the object is in an invalid state that prevents it from performing the expected action.

There are several possible causes of the IllegalStateException in Kotlin, including:

  • Calling a method or accessing a property on an object that is not properly initialized
  • Performing an operation on an object that has already been closed or released
  • Invoking a method or function in an incorrect order or sequence

To effectively handle the IllegalStateException, it is essential to identify the specific cause of the exception. This can be accomplished by examining the code and understanding the expected state of the object at the time of the exception.

Once the cause of the exception has been identified, appropriate steps can be taken to handle the IllegalStateException. Common strategies for handling this exception include:

  1. Using conditional statements to check the state of the object before performing the operation
  2. Implementing try-catch blocks to catch the IllegalStateException and handle it gracefully
  3. Providing meaningful error messages or logging statements to aid in debugging

Additionally, to prevent the IllegalStateException from occurring in the first place, it is important to ensure that proper object state management practices are followed. This includes initializing objects correctly, closing or releasing resources when they are no longer needed, and enforcing any required order or sequence of operations.

Code examples to understand how to handle Kotlin IllegalStateException >>

By understanding the causes of the IllegalStateException and employing effective handling techniques, developers can ensure that their Kotlin code operates smoothly and avoids unexpected errors due to invalid object states.

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7. Kotlin OutOfMemoryError

The Kotlin OutOfMemoryError is a runtime error that occurs when the Java Virtual Machine (JVM) cannot allocate enough memory for an object or operation. This can happen when an application consumes more memory than the JVM can provide, leading to a halt in program execution.

There are several potential causes for the Kotlin OutOfMemoryError:

  • A memory leak, where objects are not properly released and continue to occupy memory.
  • Large data structures or collections that consume excessive memory.
  • Recursive functions that create an infinite loop and exhaust the available memory.

Handling the Kotlin OutOfMemoryError requires careful management of memory usage:

  • Identify and fix any memory leaks in your code by ensuring that objects are properly released when no longer needed.
  • Optimize data structures and collections to use memory efficiently.
  • Consider using lazy initialization or caching mechanisms to minimize memory consumption.

Code examples to understand how to handle Kotlin OutOfMemoryError >>

It is also important to monitor memory usage during runtime and set appropriate limits to prevent the application from consuming excessive memory. This can be done using tools like the Java Memory Analyzer (MAT) or by monitoring JVM heap usage.

8. Kotlin SecurityException

The Kotlin SecurityException is a type of exception that is raised when a security restriction is violated or unauthorized access to system resources is attempted. This exception plays a crucial role in enforcing security measures and preventing malicious actions within your code.

There are various causes that can trigger a Kotlin SecurityException. Some common scenarios include:

  • Accessing sensitive data or system resources without proper authorization
  • Attempting to execute code from untrusted sources
  • Violating security policies or restrictions defined by the operating system or environment

When encountering a Kotlin SecurityException, it is important to handle the exception appropriately to ensure the security and integrity of your application. Here are some techniques to effectively handle security-related exceptions:

  1. Implement proper input validation and user authentication to prevent unauthorized access
  2. Use try-catch blocks to catch and handle SecurityExceptions, providing appropriate feedback and taking necessary actions
  3. Log and report security-related exceptions to analyze and investigate potential security vulnerabilities
  4. Follow security best practices, such as using secure coding techniques, encrypting sensitive data, and controlling access permissions

In addition to handling SecurityExceptions, it is essential to proactively enforce security measures in your code. Some best practices for ensuring security include:

  1. Regularly updating and patching your software to address known security vulnerabilities
  2. Using secure libraries and frameworks that have undergone rigorous security testing
  3. Adhering to security guidelines and recommendations provided by the platform or framework you are using
  4. Conducting regular security audits and assessments to identify and mitigate potential risks

Code examples to understand how to handle Kotlin SecurityException >>

By applying these techniques and best practices, you can enhance the security of your Kotlin code and protect your application and users from potential security threats.

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9. Kotlin NetworkOnMainThreadException

The Kotlin NetworkOnMainThreadException is a common exception that occurs when a network operation, such as making an HTTP request, is performed on the main thread of an Android application. This exception is thrown to prevent blocking the user interface and ensure smooth and responsive app performance.

Performing network operations on the main thread can cause the app to freeze or become unresponsive, as network requests can take a significant amount of time to complete. To avoid this issue, it is important to handle the NetworkOnMainThreadException appropriately and perform network operations asynchronously.

There are several approaches for handling the NetworkOnMainThreadException in Kotlin:

  1. Using AsyncTask: AsyncTask is a deprecated class in Android, but it can still be used for simple tasks. By executing network operations in the background thread provided by AsyncTask, you can avoid the NetworkOnMainThreadException.
  2. Using Kotlin coroutines: Coroutines are a powerful concurrency framework in Kotlin that allow for easy and efficient handling of asynchronous operations. By using coroutines, you can execute network operations on a separate thread without blocking the main thread.
  3. Using background threads: You can manually create background threads to perform network operations. This can be done using the Thread or Executor classes in Kotlin.

Code examples to understand how to handle Kotlin NetworkOnMainThreadException >>

Quote: "Performing network operations on the main thread can lead to a poor user experience, as it can cause the app to freeze or become unresponsive. It is important to handle the NetworkOnMainThreadException by executing network operations asynchronously." - Android Developer

By handling the NetworkOnMainThreadException and performing network operations asynchronously, you can ensure that your app remains responsive and provides a smooth user experience.

Best practices in handling kotlin errors

Effective error handling is essential for writing robust and reliable code in Kotlin. By following best practices, you can minimize errors and ensure that your software operates smoothly. Here are some recommended strategies for handling Kotlin errors:

  1. Use try-catch blocks: Enclose potentially error-prone code within try-catch blocks to catch and handle exceptions. This prevents the program from crashing and allows you to gracefully handle errors.
  2. Use sealed classes for error types: Sealed classes provide a concise and expressive way to define different error types in Kotlin. By using sealed classes, you can create a hierarchy of error types and handle them in a structured manner.
  3. Log and report errors: Implement proper logging and reporting mechanisms to track and diagnose errors in your code. This helps in identifying the root cause of errors and enables you to address them effectively.
  4. Provide meaningful error messages: When an error occurs, ensure that the error message provides useful information for debugging. A descriptive error message can greatly assist in troubleshooting and resolving issues.
  5. Maintain proper error-handling workflows: Define clear error-handling workflows in your code to ensure that errors are handled consistently throughout your application. This promotes code maintainability and makes it easier to debug and fix issues.

Proactive Kotlin Error Debugging with Zipy

Zipy is a powerful tool for proactive Kotlin error debugging. It offers advanced error monitoring, error tracking, and real-time error analysis features that can help you identify and resolve issues in your Kotlin application.

Using Zipy as your Kotlin error debugging tool provides several benefits:

  1. Efficient Error Monitoring: Zipy actively monitors your Kotlin application for errors, notifying you immediately when they occur. This proactive approach allows you to catch and fix errors before they impact the user experience.
  2. Comprehensive Error Tracking: Zipy provides detailed information about each error, including the component and line of code where it occurred. This enables you to quickly pinpoint the root cause of the error and implement a solution.
  3. Real-Time Error Analysis: With Zipy, you can view error logs and analyze error patterns in real-time. This helps you identify recurring errors and prioritize debugging efforts.
  4. Real User Monitoring: With Zipy, you can also capture session recordings of your users and analyze the problems they face in real-time.

Integrating Zipy into your development workflow is straightforward:

  1. Sign up for a Zipy account and obtain access to your Project SDK key and installation code.
  2. Install the Zipy package in your Kotlin application using SDK code, GTM, or via npm.
  3. You can follow the complete Zipy installation instructions here.
  4. You can contact Zipy support at or via the chat widget on our website to get any additional help for your mobile app debugging setup. 

Once integrated, Zipy will start monitoring your Kotlin application for errors and providing valuable insights for efficient debugging.

By using Zipy as your proactive Kotlin error debugging tool, you can enhance the stability and reliability of your Kotlin application, ensuring a seamless user experience.

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In conclusion, understanding and effectively handling Kotlin errors is crucial for writing robust and reliable code. By familiarizing yourself with the various Kotlin errors discussed in this article, you can better anticipate and address potential issues in your programs.

One valuable technique for managing Kotlin errors is the use of sealed classes for error types. Sealed classes allow you to define a closed set of subclasses, each representing a specific error. This approach provides clear and structured error handling, making it easier to identify and handle different types of errors.

To summarize, this article has covered several common Kotlin errors, including NullPointerException, ArrayIndexOutOfBoundsException, ClassCastException, NumberFormatException, IllegalArgumentException, IllegalStateException, OutOfMemoryError, SecurityException, and NetworkOnMainThreadException. By implementing the best practices discussed throughout the article, such as using try-catch blocks, logging and reporting errors, and providing meaningful error messages, you can enhance your Kotlin error handling skills and improve the overall quality of your code.

Now that you have a comprehensive understanding of Kotlin errors and how to handle them effectively, we encourage you to apply these strategies in your future projects. By incorporating proper error handling techniques and staying vigilant for potential issues, you can ensure a smoother and more reliable software development process.

Resources on how to debug and fix Kotlin errors

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