Java Basic Syntax: Variables and Data Types

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Java Basic Syntax: Variables and Data Types
1. Variables in Java
A variable is a name assigned to a memory location that stores a value. In Java, every variable must have a data type before it can be used.

1.1 Declaring a Variable

dataType variableName = value;

✅ Example:

int age = 25;     // Integer variable

double price = 99.99;  // Decimal number

String name = "John"; // String variable

2. Data Types in Java
Java has two types of data types:

Primitive Data Types (Stores simple values like numbers, characters, and booleans).

Reference Data Types (Stores complex objects like Arrays, Strings, and Classes).

2.1 Primitive Data Types
Data Type Size Description Example
byte 1 byte Stores integers (-128 to 127) byte b = 100;
short 2 bytes Stores integers (-32,768 to 32,767) short s = 5000;
int 4 bytes Stores integers (-2B to 2B) int num = 100000;
long 8 bytes Stores large integers long bigNum = 15000000000L;
float 4 bytes Stores decimal numbers (6-7 digits precision) float f = 5.75f;
double 8 bytes Stores decimal numbers (15 digits precision) double d = 19.99;
char 2 bytes Stores a single character char letter = 'A';
boolean 1 bit Stores true or false boolean isJavaFun = true;
✅ Example: Using Primitive Data Types

public class DataTypesExample {

    public static void main(String[] args) {

        int age = 30;

        double height = 5.9;

        char grade = 'A';

        boolean isStudent = false;



        System.out.println("Age: " + age);

        System.out.println("Height: " + height);

        System.out.println("Grade: " + grade);

        System.out.println("Is a student? " + isStudent);

    }

}

💡 Output:



Age: 30
Height: 5.9
Grade: A
Is a student? false

2.2 Reference Data Types
Reference data types store addresses of objects instead of actual values.

✅ Examples of Reference Data Types:

String

Arrays

Classes

Interfaces

✅ Example: Using Reference Data Types

public class ReferenceExample {

    public static void main(String[] args) {

        String name = "Alice";

        int[] numbers = {10, 20, 30};



        System.out.println("Name: " + name);

        System.out.println("First number: " + numbers[0]);

    }

}

💡 Output:


Name: Alice
First number: 10

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    Date: 2025-03-28 00:00:00.000000