Java Documentation Comments
The Java language supports three types of comments:
Comment Description
/* text */ The compiler ignores everything from /* to */.
// text The compiler ignores everything from // to the end of the line.
/** documentation */ This is a documentation comment and in general its called doc comment. The JDK javadoc tool uses doc comments when preparing automatically generated documentation.
This tutorial is all about explaining Javadoc. We will see how we can make use of Javadoc for generating useful documentation for our Java code.
What is Javadoc?
Javadoc is a tool which comes with JDK and it is used for generating Java code documentation in HTML format from Java source code which has required documentation in a predefined format.
Following is a simple example where red part of the code represents Java comments:
/**
* The HelloWorld program implements an application that
* simply displays "Hello World!" to the standard output.
*
* @author Zara Ali
* @version 1.0
* @since 2014-03-31
*/
public class HelloWorld {
public static void main(String[] args) {
/* Prints Hello, World! on standard output.
System.out.println("Hello World!");
}
}
You can include required HTML tags inside the description part, For example, below example makes use of <h1>....</h1> for heading and <p> has been used for creating paragraph break:
/**
* <h1>Hello, World!</h1>
* The HelloWorld program implements an application that
* simply displays "Hello World!" to the standard output.
* <p>
* Giving proper comments in your program makes it more
* user friendly and it is assumed as a high quality code.
*
*
* @author Zara Ali
* @version 1.0
* @since 2014-03-31
*/
public class HelloWorld {
public static void main(String[] args) {
/* Prints Hello, World! on standard output.
System.out.println("Hello World!");
}
}
The javadoc Tags:
The javadoc tool recognizes the following tags:
Tag Description Syntax
@author Adds the author of a class. @author name-text
{@code} Displays text in code font
without interpreting the text
as HTML markup or nested javadoc tags. {@code text}
{@docRoot} Represents the relative path to the generated document's
root directory from any generated page {@docRoot}
@deprecated Adds a comment indicating that this API should no longer be used. @deprecated deprecated-text
@exception Adds a Throws subheading to the generated documentation, with the
class-name and description text. @exception class-name description
{@inheritDoc} Inherits a comment from the nearestinheritable class or
implementable interface Inherits a comment from the
immediate surperclass.
{@link} Inserts an in-line link with visible text label that points
to the documentation for the specified package, class or
member name of a referenced class. T {@link package.class#member label}
{@linkplain} Identical to {@link}, except the link's label is displayed
in plain text than code font. {@linkplain package.class#member label}
@param Adds a parameter with the specified parameter-name followed
by the specified description to the "Parameters" section. @param parameter-name description
@return Adds a "Returns" section with the description text. @return description
@see Adds a "See Also" heading with a link or text entry
that points to reference. @see reference
@serial Used in the doc comment for a default serializable field. @serial field-description | include | exclude
@serialData Documents the data written by the writeObject( ) or
writeExternal( ) methods @serialData data-description
@serialField Documents an ObjectStreamField component. @serialField field-name field-type
field-description
@since Adds a "Since" heading with the specified since-text to
the generated documentation. @since release
@throws The @throws and @exception tags are synonyms. @throws class-name description
{@value} When {@value} is used in the doc comment of a static field,
it displays the value of that constant: {@value package.class#field}
@version Adds a "Version" subheading with the specified version-text to
the generated docs when the -version option is used. @version version-text
Example:
Following program uses few of the important tags available for documentation comments. You can make use of other tags based on your requirements.
The documentation about the AddNum class will be produced in HTML file AddNum.html but same time a master file with a name index.html will also be created.
import java.io.*;
/**
* <h1>Add Two Numbers!</h1>
* The AddNum program implements an application that
* simply adds two given integer numbers and Prints
* the output on the screen.
* <p>
* <b>Note:</b> Giving proper comments in your program makes it more
* user friendly and it is assumed as a high quality code.
*
* @author Zara Ali
* @version 1.0
* @since 2014-03-31
*/
public class AddNum {
/**
* This method is used to add two integers. This is
* a the simplest form of a class method, just to
* show the usage of various javadoc Tags.
* @param numA This is the first paramter to addNum method
* @param numB This is the second parameter to addNum method
* @return int This returns sum of numA and numB.
*/
public int addNum(int numA, int numB) {
return numA + numB;
}
/**
* This is the main method which makes use of addNum method.
* @param args Unused.
* @return Nothing.
* @exception IOException On input error.
* @see IOException
*/
public static void main(String args[]) throws IOException
{
AddNum obj = new AddNum();
int sum = obj.addNum(10, 20);
System.out.println("Sum of 10 and 20 is :" + sum);
}
}
Now, process above AddNum.java file using javadoc utility as follows:
$ javadoc AddNum.java
Loading source file AddNum.java...
Constructing Javadoc information...
Standard Doclet version 1.7.0_51
Building tree for all the packages and classes...
Generating /AddNum.html...
AddNum.java:36: warning - @return tag cannot be used in method with void return type.
Generating /package-frame.html...
Generating /package-summary.html...
Generating /package-tree.html...
Generating /constant-values.html...
Building index for all the packages and classes...
Generating /overview-tree.html...
Generating /index-all.html...
Generating /deprecated-list.html...
Building index for all classes...
Generating /allclasses-frame.html...
Generating /allclasses-noframe.html...
Generating /index.html...
Generating /help-doc.html...
1 warning
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