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Java Variables and Their Types

Java programming offers a dynamic and versatile environment for Developers. Variables are a fundamental part of this environment. But what exactly is a Java Variables? How do we declare, initialise, and use these variables in our programs? Read on to find out!

Have you ever wondered how data is stored and managed in a Java program? The answer is through variables. Without understanding the different types of Java Variables, you might end up with inefficient code or unexpected errors. Let's explore the world of Java Variables and learn how to use them effectively.

Table of Contents 

1) Learn about Variable Declaration  

2) Know About the Types of Variables in Java 

3) Differences Between the Instance Variables and the Static Variables

4) Understanding Type Conversion and Type Casting 

5) Conclusion 

Learn About Variable Declaration 

A variable declaration in Java happens once you mention the data type and give a unique name to the variable. By data type, we mean the type of data stored in this variable. Further, this variable also carries a name. An example of Syntax, as shown below, can be used to help better understand: 

Syntax:  

type variable_Name = value;

Example

int myNum = “the knowledge academy” 

Where int is the data type in Java, and myNum is the variable's name, and the knowledge academy is a value. In this way, a name can be allotted to a memory location. Values can be assigned to this variable in two ways: 

1) Initialisation 

2) Assignment

Initialisation (During Declaration)

Initialisation is the process of declaring a variable and assigning it a value in a single statement. This helps in making the code more concise and readable.

Syntax:

dataType variableName = value;

Example:

int age = 25;

Here, ‘int’ is the data type, ‘age’ is the variable name, and ‘25’ is the value assigned to the variable at the time of declaration.
 

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Assignment (After Declaration)

Assignment is the process of assigning a value to a variable after it has already been declared. This can be useful when the value to be assigned is determined later in the program.

Syntax:

variableName = value;

Example:

int age;

age = 25;

Here, ‘age’ is first declared as an ‘int’ variable without an initial value. Later, ‘25’ is assigned to the variable age.

Know About the Types of Variables in Java 

In Java, there exist different types of variables, whose characteristics are discussed in detail below:   

Types of Variables in Java

Local Variables 

a) A local variable is defined within a block, method, or constructor.

b) These variables are generated when the block begins or a function is called, and they disappear when the block leaves or the call to the function returns.

c) The scope of local variables is confined to the block in which they are declared, meaning they can only be accessed within that block.

d) It is mandatory to initialise local variables before using them within their defined scope.

Example:
 

public class LocalVariableExample {

    public static void main(String[] args) {

        // Local variable declaration and initialisation

        int sum = 0;

        // Block where local variable is used

        for (int i = 1; i <= 5; i++) {

            sum += i;

        }

        // Printing the local variable

        System.out.println("Sum: " + sum);

    }

}

 

Output: 

Sum: 15 

Instance Variables 

a) Instance variables are non-static variables that are defined in a class outside of a method, constructor, or block.

b) When a class object is created, these variables are generated and eliminated.

c) Unlike local variables, instance variables can have access specifiers. If no access specifier is provided, the default access specifier is used.

d) Initialisation of instance variables is not mandatory. They have default values based on their data type.

public class Car {

    // Instance variables

    String model;

    int year;

    // Constructor to initialise instance variables

    public Car(String model, int year) {

        this.model = model;

        this.year = year;

    }

    // Method to display car details

    public void displayDetails() {

        System.out.println("Model: " + model);

        System.out.println("Year: " + year);

    }

    public static void main(String[] args) {

        // Creating objects of Car class

        Car car1 = new Car("Toyota Corolla", 2020);

        Car car2 = new Car("Honda Civic", 2019);

        // Displaying details of car1

        car1.displayDetails();

        // Displaying details of car2

        car2.displayDetails();

    }

}

 

Output:

Model: Toyota Corolla

Year: 2020

Model: Honda Civic

Year: 2019

 

Static Variables 

a) Static variables, often known as class variables, are defined with the static keyword within a class but not in any function, constructor, or block.

b) Static variables are generated at the beginning of program execution and removed at the end.

c) Initialisation is not mandatory; default values depend on the data type (e.g., `null` for `String`, `0.0f` for `float`, `0` for `int`).
 

public class Counter {

    // Static variable

    static int count = 0;

    // Constructor that increments the static variable

    public Counter() {

        count++;

    }

    // Method to display the count

    public void displayCount() {

        System.out.println("Count: " + count);

    }

    public static void main(String[] args) {

        // Creating objects of Counter class

        Counter c1 = new Counter();

        Counter c2 = new Counter();

        Counter c3 = new Counter();

        // Displaying the count using one of the objects

        c1.displayCount();  // Output: Count: 3

    }

}

 

Output:

Count: 3

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Differences Between the Instance Variables and the Static Variables

Following is the comparison between instance variables and static variables:

Aspect

Instance Variables

Static Variables

Copies 

Each object has its own copy

Only one copy per class, shared by all objects

Memory Management

Not efficient for memory management

Good for memory management

Effect of Changes

Changes in one object do not affect others

Changes are reflected in all objects

Access

Accessed through object references

Accessed directly using the class name

Creation and Destruction

Created with the 'new' keyword and destroyed with the object

Created when the program starts and destroyed when it stops

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Understanding Type Conversion and Type Casting

Type Conversion

Type conversion is the process of converting one data type into another. This can happen either implicitly (automatically by the compiler) or explicitly (manually by the programmer).

Implicit Type Conversion (Widening Conversion):

a) When converting a smaller data type to a larger data type.

b) Done automatically by the Java compiler.

c) No data loss occurs.

int num = 10;

double d = num;  // Implicit type conversion from int to double

System.out.println(d);  // Output: 10.0

Here, the integer ‘num’ is automatically converted to a double ‘d’ without any data loss.

Type Casting

Type casting is the process of converting one data type into another explicitly. This is required when converting a larger data type to a smaller data type or when we need specific conversion logic.

Explicit Type Casting (Narrowing Conversion):

a) When converting a larger data type to a smaller data type.

b) The programmer must manually do it.

c) It might result in data loss or truncation.

double d = 10.5;

int num = (int) d;  // Explicit type casting from double to int

System.out.println(num);  // Output: 10

Here, the double ‘d’ is explicitly cast to an integer ‘num’, resulting in the truncation of the decimal part.

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Conclusion

Mastering Java Variables unlocks a new level of coding brilliance. By perfecting the art of declaring, initialising, and using local, instance, and static variables, you'll transform your code into a seamless, efficient masterpiece. Embrace these core concepts and let your Java programming skills shine!

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Frequently Asked Questions

What are the Eight Variables in Java? faq-arrow

In Java, there are eight basic data types: byte, long, float, short, int, double, char, and boolean. These types serve as the building blocks for data manipulation and storage, offering various ranges and precision.

What is the Difference Between a Variable and a Data Type? faq-arrow

Variables are named storage locations in memory that hold a value, while a data type specifies the kind of value a variable can store (e.g., int, float, String). Variables utilise data types to define their content.

What are the Other Resources and Offers Provided by The Knowledge Academy? faq-arrow

The Knowledge Academy takes global learning to new heights, offering over 30,000 online courses across 490+ locations in 220 countries. This expansive reach ensures accessibility and convenience for learners worldwide.

Alongside our diverse Online Course Catalogue, encompassing 17 major categories, we go the extra mile by providing a plethora of free educational Online Resources like News updates, Blogs, videos, webinars, and interview questions. Tailoring learning experiences further, professionals can maximise value with customisable Course Bundles of TKA.
 

What is The Knowledge Pass, and How Does it Work? faq-arrow

The Knowledge Academy’s Knowledge Pass, a prepaid voucher, adds another layer of flexibility, allowing course bookings over a 12-month period. Join us on a journey where education knows no bounds.

What are the Related Courses and Blogs Provided by The Knowledge Academy? faq-arrow

The Knowledge Academy offers various Java Courses, including Java Programming, JavaScript For Beginners, Java Engineer Training and Web Development Using Java Training. These courses cater to different skill levels, providing comprehensive insights into Career in Java.

Our Programming & DevOps Blogs cover a range of topics related to Java, offering valuable resources, best practices, and industry insights. Whether you are a beginner or looking to advance your Programming skills, The Knowledge Academy's diverse courses and informative blogs have got you covered.
 

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