Summary - Java basics

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 Main shell
javac/java: compile and run commands

Now combine all of these and write a working program yourself.

Exercise 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.

Show example solution

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello");
        System.out.println("Java 21");
    }
}

Exercise Add a comment and output

Write a Main class, a main method and two println calls. Add a // Opening comment above the first println.

Show example solution

public class Main {
    public static void main(String[] args) {
        // Opening
        System.out.println("Opening");
        System.out.println("Welcome");
    }
}

Test yourself

Match the concepts

public class

Class shell
main

Entry point
//

Comment
javac

Compiler

Complete the class skeleton

public class Main { public static ____(String[] args) { } }

Show answer

public class Main { public static void(String[] args) { } }

Next lesson: int and double

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