Starting a Java Program

Starting a Java Program

1. Steps for Absolute Beginners

1. Install JDK 17/21, check java -version.
2. Write Hello.java in Notepad/VS Code.
3. Compile: javac Hello.java → makes Hello.class.
4. Run: java Hello (no .class in command!).

2. First Program (typed, not copied)

public class Hello {
    public static void main(String[] args) {
        System.out.println("I am running Java!");
    }
}

3. What Happens Behind

Hello.java (you type) → javac (compiler) → Hello.class (bytecode) → java (JVM) → output

Error? javac: file not found → wrong folder (use cd). Main method not found → spelling of main / String[] args wrong.

4. IDE Shortcut (after command line once)

IntelliJ/Eclipse: New Project → New Class → Run button does javac+java for you. Learn command line first for exams.

5. Exam Points

• Steps javac/java with commands — 5 marks, very frequent.
• First program + output — 3 marks, frequent.
• Common errors (filename, main spelling) — 2-3 marks.