Module 1: Start Coding in Java
Common Setup Mistakes and Quick Fixes
Recognize the first errors beginners hit most often and fix them without panic.
Author
Java Learner Editorial Team
Reviewer
Technical review by Java Learner
Last reviewed
2026-04-16
Java version
Java 25 LTS
Learning goals
- Recognize a missing PATH or missing JDK problem
- Spot the wrong class name / file name mismatch
- Read compiler errors more calmly
When javac is not found: The JDK may not be installed correctly, or your PATH may not include the JDK bin directory yet.
When Java cannot find the main class: The class name may not match the file, or you may be running the command from the wrong folder.
When the compiler points at a line: Start at the line number in the error, then check the line above it too. Missing semicolons and braces often make the reported line look slightly off.
Good habit: Change one thing, rerun, and read the new error. Do not make five guesses at once.
Runnable examples
A missing semicolon
public class Main {
public static void main(String[] args) {
System.out.println("Oops")
}
}Expected output
Compiler error about a missing `;`.
A class/file mismatch
// File name: Program.java
public class Main {
public static void main(String[] args) {
System.out.println("Mismatch");
}
}Expected output
Compiler error because the public class name and file name do not match.
Common mistakes
Changing many lines before rerunning
Make one fix at a time so the next error message stays useful.
Assuming every error is a big problem
Most first-week Java errors are simple syntax or setup issues, not deep language problems.
Mini exercise
Break one small program on purpose by deleting a semicolon, read the error, then fix it.
Summary
- First errors are normal.
- Compiler messages usually point toward a concrete fix.
- One change at a time is the fastest debugging habit for beginners.
Next step
In Module 2 you will move from printing fixed text to storing values, reading input, and converting types.
Sources used