Saturday, August 05, 2006

Comments in Java Code

We all use comments to describe the Java code. There are three types if comments in Java as demonstrated in this Java tutorial by SUN:

// text

where the compiler ignores everything from // to the end of the line

/* text */

where the compiler ignores everything from /* to */ and

/** documentation */

which is ignored by the compiler the same way as the previous comment type. This one is a special comment as this indicates a documentation comment. The JDK javadoc tool uses doc comments when preparing automatically generated documentation.

I am not going to tell you how to use them. There are many articles and documentation written about that. We all know how to use them and most of us use them on a daily basis. Over time we can develop a stereotype. Mine looks like this:

/** first name */
private String firstName;

/** last name */
private String lastName;

* Constructs and returns the full name
* @return full name

public String getFullName() {
if (firstName == null) {
if (lastName == null) {
// user does not have a name specified
return "[no name]";
else {
return lastName;
else {
if (lastName == null) {
return firstName;
else {
// construct full name from first and last name
return firstName + " " + lastName;

As you can see, I use doc comments to describe the meaning and function of my class members. I also like to use line comments, rather than block comments. Even if my comment spans multiple lines I prefer to use // comments. It's due to my IDE settings. When I press Ctrl+/ it un-/comments the selected lines. It's very neat feature and I use it a lot.

Recently, I was doing some code modifications and I wanted to re-visit some code later. I decide to break the code by putting a comment in the middle if it, so it would not compile and I would be forced to come back to it.

I did somethig like this:

myObject.getAnother()/* change to ID */.getName();

To my surprise the code did not break. Even when I changed it to

myObject.getAnother()./* change to ID */getName();

Obviously, when I did this

myObject.getAnother().ge/* change to ID */tName();

the code broke. At the end I made it to break in a nice way, anyway

myObject.getAnother()./* change to ID */.getName();

(notice an extra dot)

All this made me thinking. Where are all the valid spots for the comments. After I read the definition for Java comments I understood why it worked, but I simply find it puzzling. Of course, we do not put comments in places like this, but the language allows us to.

I am not sure if there is any value in this lesson learnt. It would certainly make a good exam question though. I can see it now: "Will the following code compile?" ...


Rickard said...

My first guess would be that you can put a comment everywhere you can put linebreaks or other whitespace characters.

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sangamesh said...

Comments should be for whole class and where ever the comments needed for methods and in some special cases can add comments

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