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Datatypes in Java

Hey there! In this guide, we'll explore the different data types available in Java. Understanding data types is crucial for writing efficient and clear Java code. Let's dive in!

  • In Java, variables are containers that hold data and are defined by specifying a type followed by the variable name.
  • Variables must be declared before use and can hold various data types.

1. Declaring Variables in Java​

  • To declare a variable in Java, you specify its type, followed by the variable's name.
int age;
double salary;
char grade;

2. Initializing Variables in Java​

  • Variables can be initialized with a value at the time of declaration.
int age = 25;
double salary = 45000.50;
char grade = 'A';

3. Types of Variables in Java​

a. Integer Variables (int, byte, short, long)​

  • Holds whole numbers, both positive and negative.
int x = 10; byte y = 20;     // Range: -128 to 127
short z = 30000; // Range: -32,768 to 32,767
long w = 123456789L; // Suffix 'L' for long literals

b. Floating-Point Variables (float, double)​

  • Represents real numbers, with float using less precision than double.
float pi = 3.14f; // Suffix 'f' for float literals
double gravity = 9.81;

c. Character Variables (char)​

  • Stores a single character enclosed in single quotes.
char initial = 'A';

d. Boolean Variables (boolean)​

  • Holds either true or false values.
boolean isSunny = true;
boolean isRaining = false;

e. String Variables (String)​

  • Represents a sequence of characters, enclosed in double quotes.
String greeting = "Hello, World!";

4. Variable Scope​

  • The scope of a variable refers to the region of the program where the variable is accessible.
  • Local Variables: Declared inside methods or blocks, only accessible within that block.
  • Global Variables (Instance Variables): Declared inside a class but outside any method and accessible from any method in the class.

a. Local Variable Example:​

void myMethod() {     
    int localVar = 10;  // Only accessible inside myMethod
}

b. Global Variable Example:​

class MyClass {     int globalVar = 20;  // Accessible throughout the MyClass
    void myMethod() {
            globalVar = 30;   // Modifying globalVar
        } }

5. Constant Variables​

  • Variables declared as final cannot be modified after initialization.
final int MAX_AGE = 100;

6. Type Conversion​

Java allows conversion between data types either implicitly or explicitly (using type casting).

a. Implicit Type Conversion​

  • Java automatically converts one type to another when necessary.
int x = 10; 
double y = x;  // Implicit conversion from int to double

b. Explicit Type Conversion (Casting)​

  • You can explicitly convert a variable's type using type casting.
double pi = 3.14;
int intPi = (int) pi;  // Cast double to int

7. Dynamic Variables​

  • Variables that are allocated memory during runtime using references. Java manages memory allocation and deallocation automatically through garbage collection.
int[] arr = new int[5]; // Dynamically allocate memory for an array of integers
arr[0] = 5;