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Comments in Java

  • Comments are meta-data in a program.
  • While the code is the data, comments provide information about the code, making them meta-data.
  • Compilers ignore comments and they don't affect the execution of the program.

Types of Comments in Java

  1. Single-line comments: Denoted by //
  2. Multi-line comments: Denoted by /* ... */
  3. Documentation comments: Denoted by /** ... */

1. Single-line Comments

  • Syntax: // This is a single-line comment
  • These comments are used for short explanations or notes and don't span multiple lines.
  • Never compiles, Never included in docs.
  • Example: 
    // This is a simple single-line comment
int x = 10; // Variable initialization

2. Multi-line Comments

  • Syntax: /* This is a multi-line comment */
  • These comments span multiple lines and are useful for providing detailed descriptions.
  • Never compiles, Never included in docs.
  • Example: 
    /*
This is a multi-line comment.
It can span multiple lines without the need to use double slashes.
*/
int y = 20;

3. Documentation Comments

  • Syntax: /** This is a documentation comment */

  • Used for generating documentation with tools like Javadoc.

  • These comments can be used to explain the purpose of classes, methods, or fields in detail.

  • Javadoc comments are typically used to generate HTML documentation for Java classes.

  • Never compiles, but included in docs.

  • Example:

    /**
 * This method calculates the sum of two integers.
 * @param a First integer
 * @param b Second integer
 * @return The sum of a and b
 */
public int sum(int a, int b) {
    return a + b;
}

Javadoc Tool: The javadoc command can generate HTML, CSS, and JavaScript documentation from these comments.

javac File.java
javadoc File.java

Open Source Technology (Java as an Open Source)

  • Free License: Java can be installed and used without cost.
  • Free Libraries: Java provides a wide range of libraries for free.
  • Free Documentation: Official Java documentation is freely available.

Types of JDK (Java Development Kit)

  1. OpenJDK:

    • Open-source version of Java SE.
    • Free to use, modify, and distribute.
    • Suitable for development and personal use.

  2. Commercial JDK:

    • Provided by Oracle.
    • Required for production server use.
    • May have licensing fees for enterprise features (e.g., Java Mission Control).

Why Java is Open Source

  • Free to Use: OpenJDK is available at no cost and can be modified.
  • Community Support: Java has a strong, active open-source community.
  • Wide Adoption: Java is used widely due to its stability and scalability.