Variables and Data Types

 Declaring and Initializing Variables:

In Java, variables are used to store and manipulate data.

Let's learn how to declare and initialize variables using a simple example:

public class VariablesExample {
    public static void main(String[] args) {
        // Declaring variables
        int age;
        double height;
        boolean isStudent;

        // Initializing variables
        age = 25;
        height = 1.75;
        isStudent = true;

        // Printing variable values
        System.out.println("Age: " + age);
        System.out.println("Height: " + height);
        System.out.println("Is Student: " + isStudent);
    }
}

• In this example, we declare three variables: age of type int, height of type double, and isStudent of type boolean. We then initialize these variables with specific values.
• To access the value stored in a variable, we can use the variable's name. In this case, we print the values of the variables using the System.out.println() statement.

 3.1  Primitive Data Types: 

Java provides several primitive data types to store different kinds of information.

Here are a few commonly used ones:

• int: Used to store whole numbers, such as 42 or -10.
• double: Used to store decimal numbers, such as 3.14 or -2.5.
• boolean: Used to store either true or false.
• char: Used to store a single character, such as 'a' or '$'.

Here's an example that demonstrates the usage of these primitive data types:

public class PrimitiveDataTypesExample {
    public static void main(String[] args) {
        int age = 25;
        double height = 1.75;
        boolean isStudent = true;
        char grade = 'A';

        System.out.println("Age: " + age);
        System.out.println("Height: " + height);
        System.out.println("Is Student: " + isStudent);
        System.out.println("Grade: " + grade);
    }
}

In this example, we declare and initialize variables of different primitive data types and print their values.

 3.2  Working with Strings: 

Strings are used to represent sequences of characters in Java. They are widely used for storing text and are denoted by double quotation marks (””).

• Here's an example:

public class StringsExample {
    public static void main(String[] args) {
        String name = "CM Programming";
        String message = "Hello, " + name + "!";

        System.out.println(message);
    }
}

• In this example, we declare a variable name of type String and initialize it with the value "CM Programming".
• We then concatenate the name with a greeting message using the + operator.
• Finally, we print the concatenated message.

 3.3  Understanding Type Conversion:  

In Java, type conversion, also known as type casting, allows you to convert a value from one data type to another.

• There are two types of type conversion: implicit and explicit.
• Implicit conversion happens automatically when a value of a smaller data type is assigned to a variable of a larger data type.
• For example:

int x = 5;
double y = x;  // Implicit conversion from int to double

• Explicit conversion, on the other hand, requires manual intervention using casting.
• Here's an example:

double a = 3.14;
int b = (int) a;  // Explicit conversion from double to int using casting 

• In this example, we cast the value of a from double to int using (int).
• It's important to note that when converting between data types, you may lose precision or encounter unexpected behavior. So, be cautious when performing type conversion.

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