Comments

A comment is a note written to a human reader of a program. A comment starts with the two characters "//" (slash slash). Those characters and everything that follows them on that one line are ignored by the java compiler.

// Write three lines of a poem to the computer monitor
class Haiku
{
  public static void main ( String[] args )
  {
    System.out.println("On a withered branch" );
    System.out.println("A crow has just alighted:");
    System.out.println("Nightfall in autumn.");
  }
}

The program compiles and runs exactly the same as before. The blue in the above program was added by hand (by the author). However, some program editors (such as CodeGenie and BlueJ) are smart enough to recognize comments and will display them in color. Of course, the text file contains only the characters you have entered.