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Java Variables and Their Types: Here's All You Need to Know
Sienna Roberts 29 March 2023Java Variables are containers that hold data values, enabling efficient data storage and manipulation in a Java program. Discover how to declare, initialise, and use different types of variables. Master these fundamentals to write efficient, error-free code and elevate your Java programming skills to the next level. Read ahead!
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Table of Contents
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.
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:
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?
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?
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.
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