Writing code is an exciting process of instructing the computer to complete fantastic tasks.

Code is also read by people, and we want our intentions to be clear to humans just like we want our instructions to be clear to the computer.

Fortunately, we’re not limited to writing syntax that performs a task. We can also write comments, notes to human readers of our code. These comments are not executed, so there’s no need for valid syntax within a comment.

When comments are short we use the single-line syntax: //.

// calculate customer satisfaction rating

When comments are long we use the multi-line syntax: /* and */.

/* We chose to store information across multiple databases to minimize the possibility of data loss. We'll need to be careful to make sure it does not go out of sync! */

Another type of commenting option is the Javadoc comment which is represented by /** and */. Javadoc comments are used to create documentation for APIs (Application Programming Interfaces). When writing Javadoc comments, remember that they will eventually be used in the documentation that your users might read, so make sure to be especially thoughtful when writing these comments.

Javadoc comments are typically written before the declaration of fields, methods, and classes (which we’ll cover later in this course):

/** * The following class accomplishes the following task... */

Here’s how a comment would look in a complete program:

/** * The following class shows what a comment would look like in a program. */ public class CommentExample { // I'm a comment inside the class public static void main(String[] args) { // I'm a comment inside a method System.out.println("This program has comments!"); } }

Comments are different from printing to the screen, when we use System.out.println(). These comments won’t show up in our terminal, they’re only for people who read our code in the text editor.



The file Timeline.java has plain text information about Java.

Plain text facts aren’t valid syntax. We’ll use comments to avoid breaking the program.

Use the single-line comment syntax for the first fact.

Change this line into a comment:

Sun Microsystems announced the release of Java in 1995


Our program is still broken!

Use the multi-line syntax to make these lines into a single comment:

James Gosling is a Canadian engineer who created Java while working at Sun Microsystems. His favorite number is the square root of 2!

You should still see You are a fun language! printed!

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