We’ll cover the following
- Introduction
- Type Java Comments
- End-of-line comments
- Traditional comments, and
- Documentation comment
Introduction
A comment is the text that provides explanations of your code.
Like most other programming languages, Java lets you enter a remark into a program’s source file. The contents of a comment are ignored by the compiler. Instead, a comment describes or explains the operation of the program to anyone who is reading its source code.
Type Java Comments
Java has three basic types of comments:
- End-of-line comments,
- Traditional comments, and
- Documentation comment
End-of -line comments
An end-of-line comment or single-line comment begins with the sequence // and ends at the end of the line.
You can place an end-of-line comment at the end of any line. Programmers use single-line comments for brief, line-by-line descriptions.
Everything you type after the // is ignored by the compiler. For example:
total = total * discountPercent; // calculate the discounted total
You can also place end-of-line comments on separate lines, like this:
// calculate the discounted total
total = total * discountPercent;
You can place end-of-line comments in the middle of statements that span two or more lines. For example:
total = (total * discountPercent) // apply the discount first
+ salesTax; // then add the sales tax
Traditional comments
A traditional comment or multiline comment begins with the sequence /* , ends with the sequence */, and can span multiple lines. Anything between these two comment symbols is ignored by the compiler. As a general rule, programmers use multiline comments for longer remarks.
Here’s an example:
/*
This is a simple Java program.
Call this file "Example.java".
*/You can even insert a comment between other Java programming elements, like this:
x = (y + /* a comment */ 10) / z;
One common use for traditional comments is to add a block of comment lines at the beginning of a class to indicate information about the class – such as what the class does, who wrote it, and so on.
That type of comment, however, is usually better coded as a JavaDoc comment.
multiline comment can’t be nested.
The following code won’t compile, for example:
/*
int x, y, z;
x = 10;
y = 15;
z = (y + /* a comment */ 25) / (x+y);
*/
Here, we tried to comment out a range of lines with traditional comment.
Unfortunately, the */ sequence before 25 is interpreted as the end of the traditional comment that begins in the first line, so when the compiler encounters the */ sequence in line 6, it generates an error message.
Documentation comment
As mentioned, there are three types of comments defined by Java. You have already
seen two: single-line and multiline. The third type is called a documentation comment.
This type of comment is used to produce an HTML file that documents your program.
The documentation comment begins with a /** and ends with a */.
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