How to Use Comments in Java - dummies

By Doug Lowe

A comment in Java is a bit of text that provides explanations of your code. The compiler ignores comments, so you can place any text you want in a comment. Using plenty of comments in your programs is a good idea to explain what your program does and how it works.

Java has two basic types of comments: end-of-line comments, and traditional comments.

An end-of-line comment begins with the sequence // (a pair of consecutive slashes) and ends at the end of the line. You can place an end-of-line comment at the end of any line. Everything you type after the // is ignored by the compiler. For example:

total = total * discountPercent; // calculate the discounted total

If you want, you can also place end-of-line comments on separate lines, like this:

// calculate the discounted total
total = total * discountPercent;

You can also 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

A traditional comment begins with the sequence /*, ends with the sequence */, and can span multiple lines. Here’s an example:

/* HelloApp sample program.
   This program demonstrates the basic structure
   that all Java programs must follow. */

A traditional comment can begin and end anywhere on a line. If you want, you can even sandwich a comment between other Java programming elements, like this:

x = (y + /* a strange place for a comment */ 5) / z;