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Java Variables - Basics of Java - Software Development

In Java, variables are used to store data values that can be accessed and manipulated throughout a program. They play a crucial role in programming, allowing us to work with different types of data such as numbers, characters, and text. Understanding how to declare and use variables is fundamental when learning Java or any other programming language.

Declaring Variables

To use a variable in Java, you need to declare it first. Variable declaration involves specifying the type of data the variable will hold and giving it a name. Here's the general syntax for declaring variables:

<dataType> <variableName>;

Let's look at some examples:

int age;  // declares an integer variable named 'age'

double salary;  // declares a double variable named 'salary'

char grade;  // declares a character variable named 'grade'

String name;  // declares a String variable named 'name'

In the examples above, we declared variables of different data types, such as int, double, char, and String. The name you choose for a variable should be meaningful and related to the data it represents.

Initializing Variables

After declaring a variable, you can assign it an initial value using the assignment operator (=). Here's how it's done:

<dataType> <variableName> = <initialValue>;

Let's see some examples:

int age = 25;  // initializes the 'age' variable with the value 25

double salary = 2500.50;  // initializes the 'salary' variable with the value 2500.50

char grade = 'A';  // initializes the 'grade' variable with the value 'A'

String name = "John";  // initializes the 'name' variable with the value "John"

Note that when initializing variables, you need to provide a value that matches the data type. For example, you can't assign a string value to an integer variable.

Using Variables

Once you've declared and initialized a variable, you can use it in your code. You can perform various operations and manipulations on variables, depending on their data types.

Let's look at some examples:

int x = 5;

int y = 10;

int sum = x + y;  // performs addition and stores the result in 'sum'

System.out.println("The sum of x and y is: " + sum);


The sum of x and y is: 15

In the code snippet above, we declared three integer variables: x, y, and sum. We assigned the values 5 and 10 to x and y, respectively. Then, we added x and y together and stored the result in the sum variable. Finally, we printed the value of sum using the System.out.println() method.

Sample Problems

Problem 1: Declare a variable named radius of type double and initialize it with a value of 3.14. Compute the area of a circle using the formula area = π * radius * radius and print the result.

double radius = 3.14;

double area = Math.PI * radius * radius;

System.out.println("The area of the circle is: " + area);


The area of the circle is: 30.9744

Problem 2: Given two integer variables a and b, swap their values without using a third variable.

int a = 5;

int b = 10;

System.out.println("Before swapping: a = " + a + ", b = " + b);

a = a + b;

b = a - b;

a = a - b;

System.out.println("After swapping: a = " + a + ", b = " + b);


Before swapping: a = 5, b = 10

After swapping: a = 10, b = 5

In the code above, we perform swapping using arithmetic operations without using an additional variable. First, we add a and b and store the result in a. Then, we subtract the original value of b from a and assign the result to b. Finally, we subtract the original value of b from a to get the original value of a and assign it to a.


Variables are essential components in Java programming. They allow us to store and manipulate data, making our programs more dynamic and adaptable. Remember to declare variables, initialize them with appropriate values, and utilize them effectively in your code. With practice, you'll become comfortable working with variables and gain a solid foundation for further Java development.

The document Java Variables | Basics of Java - Software Development is a part of the Software Development Course Basics of Java.
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