Variables in Java are named memory locations used to store data that can be accessed and manipulated during program execution. Each variable is declared with a specific data type and name and can optionally be initialized with a value.

Data Type: Specifies the type of data a variable can store, such as int, double, or String.
Variable Name: Identifies the variable and must follow Java identifier rules.
Value (Optional): Can be assigned during declaration or later in the program.

Java

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);
    }
}

Output

Age: 25
Name: GeeksforGeeks
Salary: 50000.5

Declaration

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.

Initialization

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.

Java

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);                
    }
}

Output

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

Naming Rules of Java Variables

Valid Characters: Variable names can contain Unicode letters and digits, as well as _ and $, according to Java identifier rules.
Starting Character: A variable name cannot start with a digit. It must begin with a valid identifier-start character, such as a letter, _, or $.
No Reserved Keywords: Reserved Java keywords such as int, class, and if cannot be used as variable names.
Case-Sensitive: Java treats names such as age and Age as different variables.
No Spaces: Variable names cannot contain spaces.
Meaningful Names: Use descriptive names that clearly indicate the purpose of the variable, such as studentName instead of s.
Naming Convention: Use camelCase for variable names, such as totalMarks or studentAge.

Java Variables

Declaration

Initialization

Naming Rules of Java Variables

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