Variables and Data Types

Variables and data types are fundamental concepts in Java programming. They are used to store and manipulate data within a program. Let's dive into each of these concepts:

Variables

A variable is a named storage location in a computer's memory where data can be stored and retrieved during program execution. In Java, variables have a specific data type, and their type determines what kind of data they can hold.

Variable Declaration

To declare a variable in Java, you specify the variable's data type followed by its name:

dataType variableName;

For example:

int age; // Declares an integer variable named "age"
double salary; // Declares a double variable named "salary"
String name; // Declares a String variable named "name"

Variable Initialization

You can also initialize a variable at the time of declaration:

dataType variableName = value;

For example:

int age = 25; // Initializes the integer variable "age" with the value 25
double salary = 50000.50; // Initializes the double variable "salary" with the value 50000.50
String name = "John"; // Initializes the String variable "name" with the value "John"

Data Types

In Java, data types specify the type of data that a variable can hold. Java has two categories of data types: primitive data types and reference data types.

Primitive Data Types

Primitive data types are the most basic data types built into the Java language. They represent single values and are not objects. Java has eight primitive data types:

1. byte: 8-bit signed integer (-128 to 127)

2. short: 16-bit signed integer (-32,768 to 32,767)

3. int: 32-bit signed integer (-2^31 to 2^31 - 1)

4. long: 64-bit signed integer (-2^63 to 2^63 - 1)

5. float: 32-bit floating point (single precision)

6. double: 64-bit floating point (double precision)

7. char: 16-bit Unicode character (0 to 65,535)

8. boolean: Represents true or false values

Reference Data Types

Reference data types are used to store references to objects. Unlike primitive data types, reference data types do not store the actual data, but rather a reference (memory address) to where the data is stored in memory. Some common reference data types include:

- String: Represents a sequence of characters.

- Arrays: Represents a collection of elements of the same type.

Example

Here's an example demonstrating the declaration and initialization of variables using different data types:

public class Main {
    public static void main(String[] args) {
        // Primitive data types
        int age = 25;
        double salary = 50000.50;
        char gender = 'M';
        boolean isStudent = true;
        // Reference data types
        String name = "John";
        int[] numbers = {1, 2, 3, 4, 5};
    }
}

Understanding variables and data types is crucial for writing Java programs. They provide the foundation for storing and manipulating data in your programs. As you continue learning Java, you'll encounter more advanced concepts related to variables and data types, such as type casting, arrays, and objects.