1. Basic Structure of a Java Program

1.1 Overview of Java Program Components

A Java program typically consists of:

Package declaration (optional)
Import statements (optional)
Class definition
Methods and variables inside the class

1.2 Class Declaration and Syntax

Every Java program must have at least one class. The class acts as a blueprint.

class MyClass {
    // code goes here
}

1.3 Understanding Class Keywords and Naming

class keyword is used to declare a class
Class names should start with a capital letter
Example: Student, Car, HelloWorld

1.4 Structure of a Simple Java Program

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

1.5 Order of Elements in a Java File

Package declaration
Import statements
Class declaration
Variables and methods

1.6 Example Explanation

public class HelloWorld → Class name
main() → Entry point
System.out.println() → Prints output

2. The main() Method

2.1 What is the main() Method

The main() method is the starting point of every Java program.

2.2 Importance of main()

JVM starts execution from this method
Without it, the program will not run

2.3 Syntax of main()

public static void main(String[] args)

2.4 Understanding Parameters

String[] args → Command-line arguments
Allows input while running the program

2.5 Execution Flow

Program starts
JVM looks for main()
Executes statements inside it

2.6 Common Mistakes

Missing static keyword
Wrong method signature
Typo in method name

3. Packages and Imports

3.1 What is a Package

A package is a namespace that organizes related classes.

3.2 Types of Packages

Built-in packages (e.g., java.util)
User-defined packages

3.3 Creating a Package

package mypackage;

3.4 What are Import Statements

Imports allow you to use classes from other packages.

3.5 Importing Specific Classes

import java.util.Scanner;

3.6 Importing Entire Package

import java.util.*;

3.7 Static Imports

import static java.lang.Math.*;

3.8 Naming Conventions

Use lowercase
Example: com.myapp.project

4. Comments in Java

4.1 What are Comments

Comments are non-executable lines used to explain code.

4.2 Importance

Improves readability
Helps others understand code

4.3 Single-line Comments

// This is a single-line comment

4.4 Multi-line Comments

/* This is
   a multi-line comment */

4.5 Documentation Comments (Javadoc)

/**
 * This is a documentation comment
 */

4.6 Best Practices

Keep comments meaningful
Avoid unnecessary comments
Update comments with code

5. Coding Conventions

5.1 Importance

Coding conventions make code readable and maintainable.

5.2 Naming Conventions for Classes

Use PascalCase
Example: BankAccount, StudentRecord

5.3 Naming for Variables and Methods

Use camelCase
Example: totalMarks, calculateSum()

5.4 Indentation and Formatting

Use proper spacing
Keep consistent indentation

5.5 Code Readability

Use meaningful names
Avoid long and complex methods

5.6 Best Practices

Write simple and clean code
Follow standard structure
Use proper comments

5.7 Common Beginner Mistakes

Poor naming
No indentation
Writing all code in one method
Ignoring conventions

Conclusion

Understanding Java program structure is the first step toward becoming a good Java developer. Once you know how to organize your code, use the main method, manage packages, and follow coding standards, writing Java programs becomes much easier and more efficient.

Java Program Structure