Skip to main content

Structure of a Java Program

Java is a high-level, robust, secure and object-oriented programming language. It is widely used for developing web applications, software, and mobile applications. For beginners, understanding the structure of a Java program is the first stepping stone towards mastering this language. Hence, in this article, we will delve deeper into the fundamental structure of a Java program.

Basic Structure of a Java Program​

Every Java program consists of the following essential components:

  1. Documentation section: This section primarily contains a set of comments giving a brief about the program, author and time and version of the program. It's optional.

  2. Package statement: It specifies a package in which the classes are grouped together. It's optional.

  3. Import statements: These are optional, and allow us to use classes from other packages into our program.

  4. Interface statements: Interface in Java is a blueprint of a class. It's optional.

  5. Class definitions: This is a blueprint from which individual objects are created. A Java program may contain multiple classes.

  6. Main method class: Every Java standalone program requires the main method as the starting point for the program.

Here is a basic structure of a Java program:

//Documentation Section
/** 
 * Application name : HelloWorld 
 * Author : Your Name 
 * Version : 1.0 
 */

//Package Statement
package com.example; // Optional

//Import Statements
import java.util.*; // Optional

//Class Definition
public class HelloWorld {

    // Main method
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

Key Components in Detail​

Class Definition​

A class is a blueprint from which individual objects are created. In general, class declarations can include these components, in order:

  • Modifiers such as public, private, and others.
  • The class name, with the initial letter capitalized by convention.
  • The name of the class's parent (superclass), if any, preceded by the keyword extends.
  • A comma-separated list of interfaces implemented by the class, if any, following the keyword implements.
  • The class body, surrounded by braces {}.

The Main Method​

Every Java application must contain a main method whose signature looks like this:

public static void main(String[] args)

This is the entry point for any Java program. The JVM (Java Virtual Machine) will look for the main method to start executing the program.

  • public: It is an access specifier that allows the main method to be accessible everywhere.
  • static: The main method is to be called without an object. The modifiers public and static can be written in either order (public static or static public).
  • void: It means it doesn't return any value.
  • main: It's the name of the method.
  • String[]: Used for command line arguments that are an array of type string. In Java, it is possible to accept command-line arguments. E.g., java MyProgram Hello Friend. Here, "Hello" and "Friend" are command-line arguments.

Statements​

Java program statements are the instructions that tell the JVM what to do. In our sample program, System.out.println("Hello, World!"); is a statement that tells the JVM to print "Hello, World!" to the console.

In summary, understanding the structure of a Java program is essential for any beginner to get started with Java. This knowledge will serve as a foundation upon which more complex concepts can be built. Happy Learning!