Comments

// This program outputs the message "Hello World!" to the monitor
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// This program outputs the message "Hello World!" to the monitor

This is a single-line comment that documents the code. The compiler will ignore everything after//to the end of the line. Comments provide information outside the syntax of the language.

Classes

public class HelloWorld {   // class code}
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public class HelloWorld {   // class code}

This is the class of the file. All Java programs are made of at least one class. The class name must match the file: our file isHelloWorld.javaand our class isHelloWorld. We capitalize every word, a style known aspascal case. Java variables and methods are named in a similar style calledcamel casewhere every wordafter the firstis capitalized.

The curly braces,{and}, mark thescopeof the class. Everything inside the curly braces is part of the class.

Methods

public static void main(String[] args) {   // Statements  }
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public static void main(String[] args) {   // Statements  }

Every Java program must have a method calledmain(). A method is a sequence of tasks for the computer to execute. Thismain()method holds all of the instructions for our program.

Statements

System.out.println("Hello World!");
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System.out.println("Hello World!");

This code uses the methodprintln()to send the text “Hello World!” to the terminal as output.println()comes from anobjectcalledout, which is responsible for various types of output. Objects are packages of state and behavior, and they’re often modeled on real-world things.

outis located withinSystem, which is another object responsible for representing our computer within the program! We can access parts of an object with a., which is known asdot notation.

This line of code is astatement, because it performs asingletask. Statements always conclude with a semicolon.

Whitespace

Java programs allow judicious use of whitespace (tabs, spaces, newlines) to create code that is easier to read. The compiler ignores whitespace, but humans need it! Use whitespace to indent and separate lines of code. Whitespace increases the readability of your code.

Practice

The structure of a Java program will feel familiar the more you work with this language. Continue learning at Codecademy and you’ll be a Java pro in no time!

• Twitter Java Style Guide
• Google Java Style Guide

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