Introduction
As a software developer, I inevitably deal with bugs on a regular basis. Some are easy to squash, while others seem determined to avoid detection. Here are 10 of the most common software bugs I’ve encountered, along with tips on how to fix them.
Syntax Errors
These are some of the most basic bugs that occur when code is not written properly according to the rules of the programming language. For example, forgetting a semicolon at the end of a line in Java or mismatched parentheses in JavaScript would cause a syntax error.
To fix syntax errors:
- Carefully examine the line indicated by the error message
- Compare it to code examples to ensure proper syntax rules are followed
- Use an IDE with syntax highlighting to make errors more visible
Off-By-One Errors
Also known as OB1, this common bug occurs when a loop iterates one time less or more than intended. For instance, a for loop meant to repeat 10 times may only go through 9 iterations because the counter was initialized at 1 instead of 0.
To avoid off-by-one errors:
- Double check loop conditions and counter variables
- Use a debugger to step through the loop and validate the number of iterations
- Refactor loops to use .length of collections instead of hardcoded values when possible
Null Pointer Exceptions
These happen when trying to access a method or field of an object that does not exist or has not been instantiated. The most common cause is failing to check if a variable contains a valid object before calling its members.
To prevent null pointer exceptions:
- Add null checks before accessing object members
- Initialize objects properly before first use
- Use annotations that enforce null-checking if supported by your language
Resource Leaks
Any unmanaged resource like files, database connections, or network sockets must be carefully opened, used, and closed. Failing to close a resource can lead to leaks which cause system instability.
To avoid resource leaks:
- Use try-with-resources syntax or a finally block to ensure closure
- Dispose of single use objects instead of relying on garbage collection
- Use tools like heap analyzers to detect unclosed resources
Race Conditions
When asynchronous processes access and manipulate shared data improperly, race conditions can happen. For example, incrementing a global counter from multiple threads may result in incorrect counts.
To eliminate race conditions:
- Use thread-safe collections like ConcurrentHashMap
- Limit access to shared resources through synchronization
- Leverage atomic variable libraries or other high-level concurrency utilities
Heisenbugs
These bugs seem to disappear or alter behavior when you try to study them closely, just like subatomic particles change under observation. They often manifest in multi-threaded code or hardware-dependent software.
To pin down heisenbugs:
- Insert log statements to output values before, during, and after the bug manifests
- Simulate production load and environment as closely as possible
- Leverage profiling and instrumentation tools
Memory Leaks
Unlike resource leaks, these bugs occur when memory is allocated but never released after it is no longer needed. Over time, unused memory accumulates and slows down the application.
To plug memory leaks:
- Nullify object references once they are no longer needed
- Use weak references for cached objects
- Profile memory usage over time to detect increasing heap size
Unhandled Exceptions
Bugs can creep in when exceptional scenarios are not properly caught and dealt with. Uncaught exceptions crash an app and provide little contextual feedback.
To handle exceptions properly:
- Wrap risky sections in try-catch blocks
- Provide contextual logging via catch blocks
- Handle exceptions at the appropriate level
- Document expected exceptions in APIs
Infinite Loops
Debugging an app only to find it locked up and unable to accept input is maddening. Infinite loops block further execution until the process is killed.
To terminate infinite loops:
- Set loop limits and overflow checks
- Handle errors and edge cases that break loop exit conditions
- Use debuggers to pause execution and analyze stack traces
- Implement timeout limits using asynchronous code when possible
Improper Error Handling
Bugs often mimic real errors. Without proper error handling, it can be impossible to discern if an issue is a code bug or a real system failure.
To distinguish between bugs and errors:
- Handle errors with specific exception types, not generic ones
- Provide context with error logging at catch sites
- Use error codes and translate them to exceptions when needed
- Validate parameters and fail fast to avoid exceptions
Conclusion
Fixing bugs is a skill that improves with experience. Following coding best practices, using the right tools, and learning from past mistakes are the best ways to eliminate bugs. Mastering these 10 common types will lead to higher quality and more resilient software.
