Comments

Basic Syntax

Comments

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A "comment" is a message written to a human reader of the program. A comment is denoted by // at the beginning of the line. Those two characters (//) and everything that follows on the one line are disregarded by the Java compiler. Please take a look at the example below showing the use of comments.

CommentsExample.java
package exlcode;

public class CommentsExample {
  /* Comment Block

  You can write as much as you want inside the comment block

  */
  // this is another example of a comment

  public static void main (String[] args){
    // this will not print because it is a comment
    // System.out.println("Hello!");
    System.out.println("Hello World!");
  }
}

In the example above, some comments span for more than one line. To get the Java compiler to ignore multiple lines, we use /* at the beginning of the comment and */ at the end of the numerous lines of comments. When using this method to add a lengthy comment, make sure there are no characters between '/' and '*'. The /* and */ can start and stop anywhere on a line. Everything between the pair is a comment ignored by the compiler.

In addition to marking an actual comment in this way, we can also use the comment functionality for debugging. If we run into a situation where the program has a syntax error, one way to search for the root of the error is to remove some of the code from being compiled by turning it into a comment. If the modified program works as expected, the error must be in the section of code that was made into a comment. From there, we can decrease the amount of code in the comments until we pinpoint the error. Please remember this useful and important method for debugging long lines of code.

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Application Question

Which of the following lines are NOT proper Java comments?