Hello World
Print Line
System.out.println() can print to the console:
Systemis a class from the core library provided by Javaoutis an object that controls the outputprintln()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 amulti-line comment!*/
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 ☕️");
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.");}}
