Java Syntax

Introduction to Java Syntax

Java syntax refers to the set of rules that define the structure of a Java program. These rules determine how you write Java code, including classes, methods and statements. Java has a clean and organized structure that is easy to learn for beginners.

Understanding Java syntax is essential because even small syntax errors can prevent your program from running.

Basic Structure of a Java Program

Every Java program follows a specific structure. Here’s a simple example of a basic Java program:

Code Example:

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

Explanation:

1. public class HelloWorld:
   • Declares a class named HelloWorld.
   • The class name should match the filename (HelloWorld.java).
2. public static void main(String[] args):
   • The main method is the entry point of a Java program.
   • Code inside this method will execute when the program runs.
3. System.out.println(“Hello, World!”);:
   • This statement prints output to the console.
   • System.out.println is a built-in Java method.

Key Rules of Java Syntax

Case Sensitivity:

Java is case-sensitive.

• Example: HelloWorld and helloworld are different.

Class Names:

• The first letter of a class name should be uppercase.
• If the class name has multiple words, use PascalCase.
• Example:

public class MyFirstProgram { }  

Method Names:

• Method names start with a lowercase letter.
• Use camelCase for multiple words.
• Example:

public void printMessage() { }  

File Name and Class Name:

• The Java file name must match the class name.
• Save your file as ClassName.java.
• Example: If the class is HelloWorld, the file must be HelloWorld.java.

Curly Braces { }:

• Curly braces define the beginning and end of a block of code.
• Example:

public class Example {
    public static void main(String[] args) {
        System.out.println("Java Syntax");
    }
}

Semicolon ; :

• Every statement in Java ends with a semicolon.
• Missing semicolons will cause syntax errors.

Comments:

• Comments are used to explain code and are ignored by the compiler.
• Types of comments in Java:
  • Single-line comment: // This is a single-line comment
  • Multi-line comment: /* This is a multi-line comment */
  • Documentation comment: /** * This is a documentation comment * for generating API docs. */

Java Program Components

Class Declaration:

• A Java program begins with a class declaration.
• The class name must be the same as the file name.
• Example:

public class Example { }  

Main Method:

• The main() method is the entry point of every Java program.
• Syntax:

public static void main(String[] args) { }  

Statements:

• Code statements are written inside the main method.
• Each statement ends with a semicolon.
• Example:

System.out.println("Welcome to Java!");

Java Variables and Data Types

To store data in Java, variables and data types are used.

Variable Declaration Syntax:

dataType variableName = value;  

• dataType: Specifies the type of data (e.g., int, String, boolean).
• variableName: The name of the variable.

Example:

public class VariablesExample {  
    public static void main(String[] args) {  
        int number = 10; // Integer variable  
        String name = "Java"; // String variable  
        boolean isLearning = true; // Boolean variable  

        System.out.println("Number: " + number);  
        System.out.println("Name: " + name);  
        System.out.println("Learning Java: " + isLearning);  
    }  
}

Output:

Number: 10  
Name: Java  
Learning Java: true  

Java Syntax Example – Multiple Features Combined

Here is a complete program showing multiple syntax rules:

Code Example:

public class StudentDetails {  
    public static void main(String[] args) {  
        // Variable declaration  
        String name = "Alice";  
        int age = 20;  
        double marks = 85.5;  

        // Output details  
        System.out.println("Student Name: " + name);  
        System.out.println("Age: " + age);  
        System.out.println("Marks: " + marks);  
    }  
}

Explanation:

1. Variable declaration: Declares variables of type String, int and double.
2. Output: Uses System.out.println() to display variable values.

Common Syntax Errors

Missing Semicolon:

System.out.println("Hello World") // Error: Missing semicolon  

Mismatched Braces:

public class Example {
    public static void main(String[] args) {
        System.out.println("Error")  
} // Missing closing brace  

Case Sensitivity:

System.out.println("Java");  
system.out.println("Error"); // Error: System must be uppercase