Java Variables

In Java, variables are containers used to store data in memory. Variables define how data is stored, accessed, and manipulated.

A variable in Java has three components,

• Data Type: Defines the kind of data stored (e.g., int, String, float).
• Variable Name: A unique identifier following Java naming rules.
• Value: The actual data assigned to the variable.

class Geeks {
    public static void main(String[] args) {
        
        // Declaring and initializing variables
        
        // Integer variable  
        int age = 25;       
        
        // String variable  
        String name = "GeeksforGeeks"; 
        
        // Double variable 
        double salary = 50000.50;     

        // Displaying the values of variables
        System.out.println("Age: " + age);          
        System.out.println("Name: " + name);        
        System.out.println("Salary: " + salary);
    }
}

Age: 25
Name: GeeksforGeeks
Salary: 50000.5

How to Declare Java Variables?

The image below demonstrates how we can declare a variable in Java:

From the image, it can be easily perceived that while declaring a variable, we need to take care of two things that are data type of the variable and name.

How to Initialize Java Variables?

It can be perceived with the help of 3 components explained above:

Example: Here, we are initializing variables of different types like float, int and char.

class Geeks{
    public static void main(String[] args) {
        // Declaring and initializing variables
        
        // Initializing float variable
        float si = 5.5f; 
        
        // Initializing integer variables
        int t = 10; 
        int s = 20; 
        
        // Initializing character variable
        char var = 'h';               

        // Displaying the values of the variables
        System.out.println("Simple Interest: " + si);  
        System.out.println("Speed: " + s);                      
        System.out.println("Time: " + t);                        
        System.out.println("Character: " + var);                
    }
}

Simple Interest: 5.5
Speed: 20
Time: 10
Character: h

Rules to Name Java Variables

• Start with a Letter, $, or _ – Variable names must begin with a letter (a–z, A–Z), dollar sign $, or underscore _.
• No Keywords: Reserved Java keywords (e.g., int, class, if) cannot be used as variable names.
• Case Sensitive: age and Age are treated as different variables.
• Use Letters, Digits, $, or _ : After the first character, you can use letters, digits (0–9), $, or _.
• Meaningful Names: Choose descriptive names that reflect the purpose of the variable (e.g., studentName instead of s).
• No Spaces: Variable names cannot contain spaces.
• Follow Naming Conventions: Typically, use camelCase for variable names in Java (e.g., totalMarks).

Related articles:

• Scope of Variables in Java
• Types of Variables

Variables and Primitive DataTypes

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