🐞 Debugging Errors

Code not working? Follow the steps in the debugging process below before asking a peer or your teacher! Fixing your own errors, no matter how small, is one of the best ways to become a better coder.

☕ Java Debugging Process

1. Read the Error Message

   • Focus on the first error, not the dozens that follow — one small bug can cause many.
   • Look at the line number and the type of error (e.g., SyntaxError, NullPointerException).

2. Check for Missing Symbols

   • Every line (except the last in a block) needs a semicolon (;).
   • Make sure parentheses (), braces {}, and brackets [] are all paired.
   • Method headers must have parentheses: public void sayHi()

3. Check Braces and Indentation

   • Every { must have a matching }.
   • Indent code inside {} to match visually.
   • Don’t forget to close classes and methods!

4. Check Capitalization

   • Java is case-sensitive: System ≠ system, main ≠ Main
   • Classes must start with capital letters (MyClass), but variables/methods use lowercase (myVariable)

5. Check Spelling and Naming

   • Watch for typos like Systm.out.print instead of System.out.print
   • Match variable names exactly; Java won’t correct you

6. Check Data Types and Declarations

   • Make sure all variables are declared with a type (int, String, double, etc.)
   • Strings must be capitalized: String name = "Alice";

7. Print for Clarity

   • Use System.out.println() to check variable values
   • Print before and after key lines to isolate bugs

8. Compile (Press RUN) Often

   • Don’t write 50 lines without compiling. Compile frequently so you catch errors early.

9. Ask Yourself Questions

   • Is this variable initialized?
   • Am I using the correct data type for this operation?
   • Should this be inside the main method?

10. If All Else Fails…

    • Comment out blocks to isolate the issue
    • Use a visualization tool like PythonTutor.com to “step through” code, which shows what’s happening line-by-line.