Codecademy Logo

Hello World

Print Line

System.out.println() can print to the console:

  • System is a class from the core library provided by Java
  • out is an object that controls the output
  • println() is a method associated with that object that receives a single argument
System.out.println("Hello, world!"); // Output: Hello, world!

Comments

Comments are bits of text that are ignored by the compiler. They are used to increase the readability of a program.

  • Single line comments are created by using //.
  • Multi-line comments are created by starting with /* and ending with */.
// I am a single line comment! /* And I am a multi-line comment! */

main() Method

In Java, every application must contain a main() method, which is the entry point for the application. All other methods are invoked from the main() method.

The signature of the method is public static void main(String[] args) { }. It accepts a single argument: an array of elements of type String.

public class Person { public static void main(String[] args) { System.out.println("Hello, world!"); } }

Classes

A class represents a single concept.

A Java program must have one class whose name is the same as the program filename.

In the example, the Person class must be declared in a program file named Person.java.

public class Person { public static void main(String[] args) { System.out.println("I am a person, not a computer."); } }

Compiling Java

In Java, when we compile a program, each individual class is converted into a .class file, which is known as byte code.

The JVM (Java virtual machine) is used to run the byte code.

# Compile the class file: javac hello.java # Execute the compiled file: java hello

Whitespace

Whitespace, including spaces and newlines, between statements is ignored.

System.out.println("Example of a statement"); System.out.println("Another statement"); // Output: // Example of a statement // Another statement

Statements

In Java, a statement is a line of code that executes a task and is terminated with a ;.

System.out.println("Java Programming ☕️");

Related Courses

Course

Learn Java

Beginner friendly

16 Lessons
Skill Path

Build Basic Android Apps with Java

Beginner friendly

13 Lessons
Skill Path

Create REST APIs with Spring and Java

Beginner friendly

20 Lessons