Java is one of the popular programming languages. It runs everything mobile apps, big enterprise systems, cloud stuff you name it.
And with that much going on, bugs are kind of unavoidable.
What’s worse?
When you hit an error that makes zero sense, and you end up staring at your screen thinking, “Why is this happening?”
Even if you’ve been coding in Java for years, some bugs just hide well.
The good news?
Debugging doesn’t have to be this painful. With the right tools (and a bit of strategy), you can actually enjoy fixing stuff or at least not dread it.
In this post, I’ll share how I approach debugging Java apps, some tools that help a ton, and a quick look at where things are heading.
Let’s get into it.
What is Debugging in Java Today?
Debugging is just part of being a developer. Things break. You fix them. That’s how you grow.
The process involves developers finding and resolving bugs in the code so that it can run as intended. The debugging process also helps them to understand what went wrong, why the error occurred, and how to resolve it.
Debugging not only assists in bug fixes but also enhances the stability and performance of code. It used to be all System.out.println() and guesswork. Now we’ve got advanced IDEs, remote debugging, and even AI tools to help spot the issue before you do.
Key aspects of debugging in Java include:
Error Identification: Spotting runtime errors, logic flaws, and exceptions.
Root Cause Analysis: Tracing bugs back to their source with the help of tools and stack traces.
Code Optimization: Using debugging insights to improve speed, memory use, and overall efficiency.
Why Not Rely on Print Statements?
Almost all developers begin by using System.out.println() to see what’s wrong with their code. It’s easy and well-known. However, it quickly reaches its limits.
Your code may become cluttered and difficult to read if you use print statements. Particularly when working with large applications, multiple threads, or real-time data, they don’t provide you with a complete picture of what’s going on behind the scenes.
They lack flexibility as well. Unlike a proper debugger, you are unable to step through your logic, pause the program, or inspect variable values at a specific moment. They frequently only display the symptom and not the underlying cause.
For this reason, using the right debugging tools is essential to modern Java development. These enable you to delve deeper, observe memory activity, trace the code path, and address issues more quickly.
What Are Some Important Steps to Debug Java Code?
A clear debugging process helps you fix issues faster and avoid chasing the wrong problem.
Here’s how most Java developers approach it:
1. Set breakpoints
Choose which parts of your code you want to stop running. This usually happens right before a bug shows up or when you notice something odd. In most IDEs, setting a breakpoint is as easy as clicking next to the line number.
2. Run the program in debug mode
Put your app in debug mode instead of running it normally. This gives you control over how the program continues and enables the debugger to stop at breakpoints. To do this, simply click the debug icon in Eclipse or IntelliJ IDEA.
3, Step through your code
You can navigate through the program one line at a time after it pauses. To closely adhere to the reasoning, use Step into, Step Over, or Step Out. This allows you to see the exact behaviour of your code in real time.
4. Inspect variables and objects
Verify the object states, method outputs, and variable values. This lets you know what’s going on behind the scenes, such as whether an object wasn’t initialised, a condition failed, or a value is incorrect.
5. Trace the root cause
Work backwards from the failure if the bug isn’t immediately apparent. Examine method calls, track the data flow, and keep an eye out for any recent modifications. Logs and stack traces can assist you in making the connections.
6. Fix the issue and re-test
Make the required code modifications after you’ve figured it out. Then, to make sure the fix was successful and didn’t break anything else, run your program again in either debug or normal mode.
Advanced Breakpoints and Stepping Techniques
When basic breakpoints fall short, advanced tools help you trace code behavior, monitor variable changes, and pause only when specific conditions are met without slowing things down or cluttering your code with print statements.
Here are a few techniques worth knowing:
Conditional Breakpoints
These are regular breakpoints, but they only trigger if a certain condition is met. Instead of stopping every time a line runs, you can narrow it down to the exact case you care about.
Examples:
– count == 0
– user != null && user.isActive()
Most IDEs like IntelliJ or Eclipse let you right-click a breakpoint to add a condition.
Data Breakpoints (Watchpoints)
When the value of a particular variable or field changes, you can use a data breakpoint to halt the program. Finding bugs brought on by unforeseen state changes is made easier with this. They are connected to data rather than lines of code, in contrast to standard breakpoints.
Example use case: pause when orderStatus changes from “PENDING” to “CANCELLED”, even it that happens deep inside another method.
Note: Full support for data breakpoints may depend on your IDE and whether your using native debugging or JVM-level features.
Watch Expressions
Watch expressions let you keep an eye on specific values as you step through your code. They are flexible and dynamic, you can create new expressions on the fly, even combining multiple variables.
Examples:
– user.getProfile().getCountry()
– items.size() > 10
Set them up in the “Watches” pane of your IDE while debugging. They are great for observing how values evolve across iterations or method calls.
Log Points
Log points are like breakpoints, but instead of stopping the program, they just print a message to the console. They are useful when you want to trace execution without interrupting the flow:
Example (in IntelliJ):
“Reached line with item: ” + item.getName()
Unlike print statements, they don’t require code changes; you can add or remove them directly from the debugger, which keeps your codebase clean.
Particularly in larger projects or unknown codebases, these tools provide a much clearer picture of what your code is doing and are quick to set up.
What Are the Modern Tools for Java Debugging?
For debugging, the majority of Java developers use IDEs like IntelliJ IDEA or Eclipse, but an expanding collection of tools and plugins provide greater flexibility, improved visibility, and more efficient workflows, particularly in larger or distributed systems.
Here are some modern tools worth exploring:
1. IntelliJ IDEA Debugger
IntelliJ has a solid debugger built right into the IDE. It moves quickly, smoothly, and without obstructing your path. You don’t have to look elsewhere to figure out what’s wrong if you are already coding in IntelliJ.
Developers love it because it:
- Shows variable values right inside the code while debugging
- Smart step options that skip over boilerplate methods
- Easily set conditions or log outputs at breakpoints
- Works well with Docker, remote setups, and complex projects
- Handles multi-threaded code without slowing down
2. Eclipse Debugger
Eclipse is still widely used in business settings, and its debugger is still a good option. Compared to IntelliJ, it might seem a little outdated, but it has strong debugging capabilities and fine-grained control over threads, breakpoints, and execution flow.
What makes it useful:
- Customizable breakpoints with conditions and hit counts
- Watchpoints for monitoring variable access and modification
- Full control over thread suspension, resume, and inspection
- Built-in support for debugging remote applications
- Well-documented and supported by large enterprise teams
3. VisualVM
The JDK comes with a monitoring and profiling tool called VisualVM. It is extremely helpful in locating memory leaks, CPU spikes, or slow threads in production or staging, but it is more suited for performance diagnostics than line-by-line debugging.
Where it shines:
- Attaches to local or remote JVMs to inspect live data
- Heap dump analysis for identifying memory leaks
- Built-in CPU profiler to find bottlenecks
- Thread monitoring with real-time status and stack traces
- Can be extended with plugins for deeper insights
4. JDB (Java Debugger)
The JDK includes a command-line debugger called JDB. It’s simple and text-based, making it a good choice when you’re working on servers without a GUI or running automated scripts in a lightweight setup.
Why it’s still relevant:
- No setup needed it just works from the command line
- You can inspect variables, control flow, and set breakpoints straight from terminal
- Perfect when working on remote servers or CI pipelines
- Easy to script if you’re automating tests or workflows
- Lightweight and doesn’t hog memory ideal for constrained environments
5. Chrome DevTools for Java (via GraalVM or JPro)
Some newer frameworks allow Java to run in the browser, compiled down to WebAssembly, and when that happens, you can actually use Chrome DevTools to debug the Java code. It’s niche, but powerful for certain types of front-end Java applications.
Why it’s worth knowing:
- Lets you step through Java code inside Chrome just like JavaScript
- View variables, call stacks, and breakpoints using a familiar UI
- Mostly useful for client-side UIs built with Java (like JPro apps)
- Requires setup with GraalVM or specific frameworks
Final Thoughts
Debugging isn’t something you master overnight.
Every bug is a little different, and every time you fix one, you get sharper.
You start noticing patterns, trusting your instincts, and choosing smarter paths when things go wrong.
Whether you’re deep into a Java project or just starting out, the more bugs you squash, the better you get at solving them fast and with confidence.
So if you are working on a project or planning to hire a Java developer, knowing these best techniques can help everyone work faster with fewer surprises.
