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The multi-line comment style is particularly useful for creating large blocks of information that should be ignored by the compiler. This style can be used to produce a comment consisting of a single line of text as well. However, the single-line comment style discussed in the next section requires less typing.
Single-line comments
Single-line comments begin with // and end at the end of the line. The compiler ignores the // and everything following the slash characters to the end of the line.
This style is particularly useful for inserting short comments throughout the source code. In this case, the // can appear at the beginning of the line as shown in Figure 1 , or can appear anywhere in the line, including at the end of some valid source code (also shown in Figure 1 ) .
The purpose of the program named Comments01 , which is shown in Listing 3 near the end of the module, is to illustrate the use of single and multi-line comments. The program does not contain any javadoc comments.
The commands for a batch file that you can use to compile and run this program are provided in Listing 4 .
When you compile and run the program, the following text should appear on your command-line screen:
Hello World
I will explain this program in fragments, and will explain only those portions of the program that are germane to this module. Don't worry about the other details of the programat this time. You will learn about those details in future modules.
A multi-line comment
Listing 1 , shows a multi-line comment, which consists of three lines of text.
As required, this multi-line comment begins with /* and ends with */. The extra stars on the third line are simply part of the comment.
You will often see formats similar to this being used to provide a visual separation between multi-line comments and the other parts of a program.
| Listing 1 . A multi-line comment. |
|---|
/*File Comments01.java
This is a multi-line comment.*****************************************/ |
Single-line comments
Listing 2 shows three single-line comments. Can you spot them? Remember, single-line comments beginwith //.
| Listing 2 . Three single-line comments. |
|---|
class Comments01 {
//This is a single-line commentpublic static void main(String[] args){System.out.println("Hello World");
}//end main}//End class |
One of the comments in Listing 2 starts at the beginning of the line. The other two comments follow some program code.
I encourage you to run the program that I presented in this lesson to confirm that you get the same results. Experiment withthe code, making changes, and observing the results of your changes. Make certain that you can explain why your changes behave as they do.
Listing 3 contains a complete listing of the program named Comments01 .
| Listing 3 . The program named Comments01. |
|---|
/*File Comments01.java
This is a multi-line comment.*****************************************/
class Comments01 {//This is a single-line comment
public static void main(String[]args){
System.out.println("Hello World");}//end main
}//End class |
Listing 4 contains the commands for a batch file that can be used to compile and run the program named Comments01 .
| Listing 4 . Batch file to compile and run the program named Comments01. |
|---|
echo off
clsdel *.class
javac -cp .; Comments01.javajava -cp .; Comments01
pause |
This section contains a variety of miscellaneous information.
Financial : Although the Connexions site makes it possible for you to download a PDFfile for this module at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should be aware thatsome of the HTML elements in this module may not translate well into PDF.
I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.
In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.comshowing me as the author. I neither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, pleasebe aware that it is a copy of a module that is freely available on cnx.org and that it was made and published without my prior knowledge.
Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.
-end-
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