Java Variables and Literals

What is a Variable?

A variable is a container that stores data in your program. Think of it like a labeled box where you can put information, use it later, and even change what's inside. Every variable has three things: a name, a type (what kind of data it holds), and a value (the actual data).

• Name: What you call your variable (like myAge, studentName)
• Type: What kind of data it stores (numbers, text, true/false)
• Value: The actual data stored inside the variable

Declaring and Using Variables

To use a variable, you must first declare it by specifying its type and name. You can also assign a value right away.

public class VariableExample {
    public static void main(String[] args) {
        // Declaring and initializing variables
        int age = 20;                      // Integer (whole number)
        double height = 5.8;               // Decimal number
        String name = "Alice";             // Text
        boolean isStudent = true;          // True or False
        
        // Printing the variables
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Height: " + height);
        System.out.println("Is Student: " + isStudent);
        
        // Changing variable values
        age = 21;
        System.out.println("Updated Age: " + age);
    }
}

Name: Alice
Age: 20
Height: 5.8
Is Student: true
Updated Age: 21

Explanation:

• int age = 20; - Creates a variable named "age" of type int (integer) and assigns it the value 20
• double height = 5.8; - Creates a decimal number variable named "height"
• String name = "Alice"; - Stores text inside the variable "name"
• boolean isStudent = true; - Stores a true/false value
• age = 21; - You can change what's stored in a variable by assigning a new value

What is a Literal?

A literal is a fixed value written directly in your code. It's the actual data you write, not a container. For example, when you write "20" directly in code, that 20 is a literal. Literals are the real values, while variables are containers that hold those values.

• Integer Literal: 10, 100, -5 (whole numbers)
• Decimal Literal: 3.14, 5.8, 0.5 (numbers with decimals)
• String Literal: "Hello", "Java", "CrackEase" (text in quotes)
• Boolean Literal: true, false (only two values)
• Character Literal: 'A', 'x', '9' (single character in quotes)

Literals in Action

Here's how literals work directly in code:

public class LiteralExample {
    public static void main(String[] args) {
        // Integer Literals (no decimal point)
        int score = 95;              // 95 is a literal
        int count = -10;             // -10 is a literal
        
        // Double Literals (with decimal point)
        double price = 19.99;        // 19.99 is a literal
        double pi = 3.14159;         // 3.14159 is a literal
        
        // String Literals (text inside quotes)
        String message = "Welcome to Java!";  // "Welcome to Java!" is a literal
        
        // Boolean Literals (only true or false)
        boolean isPassed = true;     // true is a literal
        boolean isFailure = false;   // false is a literal
        
        // Character Literals (single character in single quotes)
        char grade = 'A';            // 'A' is a literal
        
        // Direct literals in print statements
        System.out.println(100);           // 100 is used directly as a literal
        System.out.println("Score: " + score);
        System.out.println("Price: $" + price);
    }
}

100
Score: 95
Price: $19.99

Explanation:

• Every number, text, or value you write directly in code is a literal
• The variable stores the literal value, but you can reuse it later
• Literals give variables their initial values
• You can use literals anywhere you need a fixed value

Common Variable Types

Rules for Naming Variables

Java has rules about what you can name your variables. Follow these to write clean code:

• Start with a letter: Use a letter (a-z, A-Z), underscore (_), or dollar sign ($)
• No spaces: Variable names cannot have spaces
• Case-sensitive: age, Age, and AGE are three different variables
• No special characters: Don't use symbols like @, #, %, &
• Use meaningful names: Write studentName instead of sn for clarity
• camelCase is standard: Start lowercase, capitalize first letter of next words (myFirstName)