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Hajipur, Bihar, 844101
Java Syntax
Before writing complex programs in Java, it’s important to understand its basic syntax. The syntax defines how Java code is written and structured so that the compiler can interpret it correctly. If you’ve worked with C or C++ before, Java’s syntax will feel familiar. But even for beginners, Java is designed to be simple, readable, and organized.
In this tutorial, we’ll walk through the structure of a Java program, rules for naming and writing code, and the role of statements, variables, and data types.
Structure of a Java Program
Every Java program follows a particular structure. Let’s look at the basic format using a simple example:
class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello, Java Syntax!");
}
}
Let’s break this down step by step:
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class HelloWorld – Every Java program must have at least one class. The class name should match the filename. For example, if your class is
HelloWorld, the file name must beHelloWorld.java. -
public static void main(String[] args) – This is the entry point of the program. The main method is where the execution starts.
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publicmeans it can be accessed from anywhere. -
staticallows the method to run without creating an object. -
voidmeans it does not return any value. -
String[] argsaccepts command-line arguments.
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System.out.println("Hello, Java Syntax!"); – This line prints output on the screen.
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Curly braces
{ }– Define the beginning and end of blocks, such as a class or method. -
Semicolon
;– Every statement must end with a semicolon.
Java Case Sensitivity
Java is a case-sensitive language, which means uppercase and lowercase letters are treated differently.
For example:
System.out.println("Hello");
system.out.println("World");
The first line works fine, but the second will cause an error because System should always start with a capital ‘S’.
Java Comments
Comments are ignored by the compiler but help you describe what the code does. They improve readability, especially in large projects. Java supports three types of comments:
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Single-line comment
// This is a single-line comment -
Multi-line comment
/* This is a multi-line comment */ -
Documentation comment
/** This comment is used for generating documentation */
Java Identifiers
Identifiers are the names you use for classes, variables, methods, and other elements. There are specific rules for naming them:
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Must start with a letter, underscore (_), or dollar sign ($).
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Cannot start with a number.
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Cannot use Java reserved keywords like
class,int,public, etc. -
Names are case-sensitive.
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Should be meaningful and follow camelCase for variables and methods.
Examples of valid identifiers:
studentName, totalMarks, _result, $price
Invalid identifiers:
2value, total-marks, class
Java Keywords
Java has a set of reserved keywords that have predefined meanings and cannot be used as identifiers.
Examples include:
class, public, static, void, if, else, while, for, return, int, double, new, try, catch, extends, this, and many more.
These keywords form the core grammar of the Java language.
Java Variables
Variables store data that can be used and changed during program execution. Each variable in Java must be declared with a specific data type.
Syntax:
dataType variableName = value;
Example:
int age = 22;
String name = "Priya";
Rules for variables:
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Must be declared before use.
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Must have a valid identifier.
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The value can be changed later if not declared as
final.
Java Data Types
Java is a statically typed language, meaning every variable’s type must be known at compile time. Data types define what kind of data a variable can store.
1. Primitive Data Types
These are built-in and directly supported by Java.
| Type | Size | Example |
|---|---|---|
| byte | 1 byte | byte num = 10; |
| short | 2 bytes | short val = 200; |
| int | 4 bytes | int count = 5000; |
| long | 8 bytes | long bigNum = 100000L; |
| float | 4 bytes | float rate = 5.5f; |
| double | 8 bytes | double price = 99.99; |
| char | 2 bytes | char grade = 'A'; |
| boolean | 1 bit | boolean isActive = true; |
2. Non-Primitive Data Types
These are objects and include:
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Strings
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Arrays
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Classes
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Interfaces
Example:
String city = "Delhi";
Java Statements and Blocks
A statement is a single line of code that performs a specific task, such as declaring a variable or printing output. Each statement ends with a semicolon.
Example:
int x = 10;
System.out.println(x);
A block is a group of statements enclosed within curly braces { }.
Blocks are used in loops, methods, and classes.
Example:
{
int a = 5;
int b = 10;
System.out.println(a + b);
}
Java Whitespace and Indentation
Java ignores extra spaces, tabs, and newlines, but proper indentation makes your code easier to read.
Example:
System.out.println("Hello"); // readable
vs
System.out.println("Hello");
Both work, but the first is cleaner when code is longer.
Java Naming Conventions
Following naming conventions makes your code consistent and professional.
| Element | Convention | Example |
|---|---|---|
| Class | PascalCase | StudentDetails |
| Method | camelCase | calculateMarks() |
| Variable | camelCase | totalAmount |
| Constant | UPPER_CASE | MAX_SPEED |
Example Program: Variables and Data Types
class StudentInfo {
public static void main(String[] args) {
String name = "Aarohi";
int age = 20;
double marks = 85.6;
boolean passed = true;
System.out.println("Student Name: " + name);
System.out.println("Age: " + age);
System.out.println("Marks: " + marks);
System.out.println("Passed: " + passed);
}
}
Output:
Student Name: Aarohi
Age: 20
Marks: 85.6
Passed: true
This program shows how variables, data types, and syntax rules come together in a simple Java code.
Summary of the Tutorial
In this chapter, you learned the basic structure of a Java program, how to declare variables, use data types, and follow syntax rules. Understanding syntax is the first step to writing clean and error-free Java programs. Every symbol, keyword, and convention plays a role in making your code understandable for both the compiler and other developers.
In the next tutorial, we’ll explore Java Output, where you’ll learn different ways to display information on the screen using print() and println() methods.
Practice Questions
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What is the basic structure of a Java program?
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Why must the class name and filename match in Java?
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What is the purpose of the
main()method in a Java program? -
Why is Java considered a case-sensitive language?
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What are the different types of comments supported in Java?
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What are identifiers in Java, and what rules should be followed while naming them?
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What are Java keywords, and why can’t they be used as identifiers?
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What is the difference between primitive and non-primitive data types in Java?
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What is the importance of semicolons and curly braces in Java syntax?
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What naming conventions should be followed for classes, variables, and methods in Java?
