Section 9.1 Mistakes Happen!
Making mistakes is a very natural part of learning Java—or any other programming language. In fact, mistakes are an absolutely essential part of the learning process! So, try not to feel discouraged when you encounter errors in your code. Instead, view each mistake as an opportunity to deepen your understanding. Every programmer, no matter how experienced, encounters errors in their code. The key is to learn how to identify and correct these errors while also learning from them.
The good news is that most errors happen for just a few common reasons, and once you recognize the patterns, they become much easier to fix. This chapter focuses on those typical mistakes and how to understand and correct them.
One of the best ways to correct these errors is to slow down and test your code in small pieces. Write a few lines, compile, and check the output before moving on. If something goes wrong, read the first error message very carefully, and focus on fixing one problem at a time. Often, solving the first error helps fix others that follow.
A simple debugging technique is to use
System.out.println() to print out variable values. If you’re not sure whether a part of your code is running correctly or what a variable contains, you can print it out. This can help you to check your assumptions and narrow down where something is going wrong.
Consider the following example where we have a method that multiplies a number by two. We can add print statements to help us debug the code:
In the example above,
System.out.println() is used inside both main and multiplyByTwo() to trace what values are being passed and returned. This kind of print-based debugging can quickly reveal logic errors, unexpected behavior, or whether a method is even being called. However, overuse of this technique will often take more time than using the debugging tools that are built into your IDE.
Useful tools in the built-in Java debugger can help you step through your code, inspect variables, and evaluate expressions at runtime. Familiarizing yourself with these tools can greatly enhance your debugging efficiency.
Above all, when you encounter an error, be patient with yourself. Every mistake you make is an opportunity to learn.
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