Java Basic Syntax - Java Technology | BigXStar

Java Program Structure

Every Java program follows a specific structure. Let's look at the anatomy of a basic Java program:

java

// This is a single-line comment

/*
 * This is a multi-line comment
 * It can span multiple lines
 */

package com.bigxstar.tutorial; // Package declaration (optional)

import java.util.Scanner;      // Import statement (as needed)

public class MyProgram {       // Class declaration

    public static void main(String[] args) {  // Main method
        System.out.println("Welcome to Java!"); // Statement
    }
}

Key Syntax Rules

1. Case Sensitivity

Java is case-sensitive. myVariable, MyVariable, and MYVARIABLE are all different identifiers.

java

int age = 25;       // valid
int Age = 30;       // different variable
int AGE = 35;       // yet another different variable

2. Class Name

Every Java program must have at least one class
The class name must match the filename (for public classes)
Class names should be in PascalCase (e.g., MyFirstProgram)

java

// File: MyFirstProgram.java
public class MyFirstProgram {
    // ...
}

3. Main Method

The main method is the entry point of every Java application. The JVM looks for this exact signature:

java

public static void main(String[] args) {
    // Your code starts here
}

Keyword	Meaning
`public`	Accessible from anywhere
`static`	Can be called without creating an object
`void`	Returns nothing
`main`	Method name (JVM looks for this)
`String[] args`	Command-line arguments

4. Statements and Semicolons

Every statement in Java must end with a semicolon ;

java

System.out.println("Hello");   // ✓ Correct
int x = 10;                     // ✓ Correct
// System.out.println("Hello")  // ✗ Missing semicolon — compile error

5. Blocks and Braces

Code blocks are enclosed in curly braces { }:

java

public class Example {                    // Class block
    public static void main(String[] args) { // Method block
        if (true) {                        // If block
            System.out.println("Inside block");
        }
    }
}

Comments in Java

Comments are ignored by the compiler and are used to document your code.

Single-Line Comment

java

// This is a single-line comment
int age = 25; // You can also add comments at end of a line

Multi-Line Comment

java

/*
 * This is a multi-line comment.
 * Use it for longer explanations.
 */

Javadoc Comment

Used to generate API documentation:

java

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

Java Keywords

Java has 67 reserved keywords that cannot be used as identifiers. Some common ones:

Category	Keywords
Data Types	`int`, `float`, `double`, `char`, `boolean`, `long`, `short`, `byte`
Control Flow	`if`, `else`, `switch`, `case`, `for`, `while`, `do`, `break`, `continue`
Access Modifiers	`public`, `private`, `protected`
Class-Related	`class`, `interface`, `extends`, `implements`, `abstract`
Object	`new`, `this`, `super`, `instanceof`
Exception	`try`, `catch`, `finally`, `throw`, `throws`
Other	`return`, `void`, `static`, `final`, `import`, `package`

Naming Conventions

Java follows specific naming standards:

Element	Convention	Example
Class	PascalCase	`StudentRecord`, `HashMap`
Method	camelCase	`calculateTotal()`, `getName()`
Variable	camelCase	`firstName`, `totalCount`
Constant	UPPER_SNAKE_CASE	`MAX_SIZE`, `PI`
Package	all lowercase	`com.bigxstar.utils`

Printing Output

Java provides several ways to print output:

java

public class OutputDemo {
    public static void main(String[] args) {
        // println — prints with a new line
        System.out.println("Hello, World!");
        System.out.println("This is on a new line.");

        // print — prints without a new line
        System.out.print("Hello ");
        System.out.print("World!");
        System.out.println(); // Just a new line

        // printf — formatted output
        String name = "Java";
        int version = 21;
        System.out.printf("Welcome to %s version %d%n", name, version);
    }
}

Output:

Hello, World!
This is on a new line.
Hello World!
Welcome to Java version 21

Reading Input

Use the Scanner class to read user input:

java

import java.util.Scanner;

public class InputDemo {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter your name: ");
        String name = scanner.nextLine();

        System.out.print("Enter your age: ");
        int age = scanner.nextInt();

        System.out.printf("Hello %s, you are %d years old.%n", name, age);

        scanner.close();
    }
}

Output:

Enter your name: Arjun
Enter your age: 22
Hello Arjun, you are 22 years old.

Complete Example

Here's a program that demonstrates multiple syntax concepts:

java

package com.bigxstar.tutorial;

import java.util.Scanner;

/**
 * A simple temperature converter program.
 * Demonstrates basic Java syntax, input/output, and variables.
 */
public class TemperatureConverter {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Get temperature in Celsius
        System.out.print("Enter temperature in Celsius: ");
        double celsius = scanner.nextDouble();

        // Convert to Fahrenheit
        double fahrenheit = (celsius * 9.0 / 5.0) + 32;

        // Display result
        System.out.printf("%.1f°C = %.1f°F%n", celsius, fahrenheit);

        scanner.close();
    }
}

Output:

Enter temperature in Celsius: 37
37.0°C = 98.6°F

Summary

Java programs must have a class with a main method as the entry point
Java is case-sensitive and every statement ends with a semicolon
Code blocks are enclosed in curly braces { }
Follow Java naming conventions: PascalCase for classes, camelCase for methods/variables
Use System.out.println() for output and Scanner for input
Java has three types of comments: single-line (//), multi-line (/* */), and Javadoc (/** */)
There are 67 reserved keywords that cannot be used as variable names