Adding/Writing Comments in Java, Comment types with Examples

Adding/Writing Comments in Java:

In this post, We will learn about how to add comments in Java and its significance.

In Java, Comments are allowed to use in addition to the executable declarations and statements i.e. what ever we write code in the class or methods. These are very helpful for better understanding of what code does and not processed by the java compiler. Because, compiler knows it is just comment which is being used for humans understanding (Compiler ignores it). Comments can be written at any part of the class.

More on Core Java

Variable Types
Identifiers and Keywords
Import, Static Import
Packages
Constructor in Java, Types, Examples, Purpose

Can write comments before package statement?

Yes. It is legal to use.

// Comment before package

package blog.java.w3schools.comments;

public class CommentsDemo {
 public static void main(String[] args) {
  System.out.println("Comments demo in java");
 }
}

Output:

Comments demo in java

As per the Oracle official website, It is mainly refereed as Java Doc.

Comment Types in Java:

Java supports three types of comments.

1) In-line Comments
2) Block Comments
3) Documentation Comments.

1) In-line Comments:

Any line starts with "//" then it is said to be In-line comment and till end of the line is considered as comment. Anything is written in the next line, compiler treats as next statement.

If we want to write comment only one line then In-Line comments are useful. Mainly written just before/after any statement.

In-line Comments Example:

package blog.java.w3schools.comments;

public class InlineCommentsExample {

 // The value is used for character storage.
 private final char value[] = new char[10];

 // Cache the hash code for the string
 private int hash; // Default to 0

 // use serialVersionUID from JDK 1.0.2 for interoperability
 private static final long serialVersionUID = -6849794470754667710L;

 // Main Method.
 public static void main(String[] args) {
  // Inside main method. This is Inline comment example program.
  System.out.println("In-line Comments Example");
 }
}

Output:

In-line Comments Example

2) Block Comments:

Any line or set of lines in java program starts with "/*" and ends with "*/" then it is called as Block Comments.
Mainly these are useful to comment multiple lines of code or some informative text. If we want, not execute a few lines of code just put them inside block comments.

Block Comments Example Program:

public class BlockCommentsExample {

 public static void main(String[] args) {
  int count = 0;
  /* I do not want to execute these line when my program runs.
     So I use block comment here.
     count = count + 1;
     count = count + 1;
   */
  
  count = count + 1;
  count = count + 1;
  System.out.println("block Comments Example: count value: "+count);
 }
}

Output:

block Comments Example: count value: 2

If all lines are executed then count value should be 4 but seeing count is 2. Because two statements are inside block comments.

3) Documentation Comments:

Documentation Comments starts with "/**" and ends with "*/" as similar to the block comments. We can include annotation inside documentation comments. These type comments can be applied to the class or method level.

Documentation Comments Example code:

/**
     * Compares this string to the specified object.  The result is {@code
     * true} if and only if the argument is not {@code null} and is a {@code
     * String} object that represents the same sequence of characters as this
     * object.
     *
     * @param  anObject
     *         The object to compare this {@code String} against
     *
     * @return  {@code true} if the given object represents a {@code String}
     *          equivalent to this string, {@code false} otherwise
     *
     * @see  #compareTo(String)
     * @see  #equalsIgnoreCase(String)
     */
    public boolean equals(Object anObject) {
        if (this == anObject) {
            return true;
        }
        if (anObject instanceof String) {
            String anotherString = (String)anObject;
            int n = value.length;
            if (n == anotherString.value.length) {
                char v1[] = value;
                char v2[] = anotherString.value;
                int i = 0;
                while (n-- != 0) {
                    if (v1[i] != v2[i])
                        return false;
                    i++;
                }
                return true;
            }
        }
        return false;
    }

Summary:

Comments are prominently used in all programming languages not execute a line or few lines of code and giving signal to compiler to ignore these set of statements.

Please leave your questions or comments in the comment section.

Java Doc Tool
Java Comments Examples