Summary - Java basics
- Java course
- Beginner
- Lesson 6/116
- 5 min
Combine main, comments and the class skeleton to write your first Java program.
Summary - Java basics
In this group you learned the basic building blocks of Java:
- Java: compiled, object-oriented, platform-independent language
- main method: the entry point of a program
- Comments: explanation for humans with
//and/* */ - Class skeleton: the
public class Mainshell - javac/java: compile and run commands
Now combine all of these and write a working program yourself.
Practice Write a two-line program
Define a Main class with a main method. From main, print Hello first and Java 21 second with two println calls.
Sample solution
public class Main {
public static void main(String[] args) {
System.out.println("Hello");
System.out.println("Java 21");
}
}Expected output
Hello Java 21
Practice Add a comment and output
Write a Main class, a main method and two println calls. Add a // Opening comment above the first println.
Starter code
public class Main {
}Sample solution
public class Main {
public static void main(String[] args) {
// Opening
System.out.println("Opening");
System.out.println("Welcome");
}
}Expected output
Opening Welcome
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the concepts
| Term | Meaning |
|---|---|
public class |
Class shell |
main |
Entry point |
// |
Comment |
javac |
Compiler |
2 Complete the class skeleton
Question
public class Main { public static ____(String[] args) { } }
Answer
public class Main { public static void(String[] args) { } }Explanation: main returns no value.