Troubleshooting: Common First-Time Errors

Error 1: javac: command not found or 'javac' is not recognized...

• Meaning: Your operating system's terminal cannot find the javac compiler program.

• Cause: The directory containing the JDK's bin folder (where javac.exe and java.exe live) is not in your system's PATH environment variable.

• Fix: You need to add the full path to your JDK's bin directory (e.g., C:\Program Files\Java\jdk-21\bin) to your system's PATH variable. After adding it, you must close and reopen your terminal for the change to take effect.

Error 2: Error: Could not find or load main class ...

• Meaning: The java command found the .class file, but it couldn't find a valid main method inside it, or you are in the wrong directory.

• Common Causes & Fixes:

• Wrong Directory: Make sure you are running the java command from the directory that contains your .class file.

• Incorrect Class Name: If your class is public class MyProgram, you must run java MyProgram. Case matters!

• Incorrect main method signature: The signature must be exactly public static void main(String[] args). Any typo (e.g., Main, string, VOID) will cause this error.

Error 3: Syntax Errors (e.g., error: ';' expected)

• Meaning: The compiler (javac) found a mistake in your Java grammar.

• Cause: These are typos. Common ones include missing semicolons ; at the end of statements, missing curly braces { or } for classes and methods, or mismatched parentheses ( or ).

• Fix: Read the error message carefully! The compiler usually tells you the exact line number where it got confused. Go to that line and look for the mistake.

Mini-Exercise: Intentionally make one of the errors above in your HelloWorld.java file. For example, delete a semicolon. Try to compile it and see the error message. Then, fix it and compile again.

// Code with a syntax error (missing semicolon)
public class ErrorExample {
    public static void main(String[] args) {
        System.out.println("This will cause a compiler error")
    }
}