Dart Static Members

Key Static Concepts

static String className = 'MyClass';

MyClass.staticMethod();

static int sharedCounter = 0;

static double calculateArea(r) => 3.14 * r * r;

🔹 Static Variables

Static variables are shared across all instances of a class:

class Student {
  String name;
  static int totalStudents = 0;  // Static variable
  static String schoolName = 'ABC School';  // Static variable
  
  Student(this.name) {
    totalStudents++;  // Increment when new student is created
  }
  
  void displayInfo() {
    print('Name: $name');
    print('School: $schoolName');
    print('Total students: $totalStudents');
  }
  
  // Static method to get school info
  static void displaySchoolInfo() {
    print('School: $schoolName');
    print('Total students enrolled: $totalStudents');
  }
}

void main() {
  // Access static variable without creating object
  print('Initial count: ${Student.totalStudents}'); // Initial count: 0
  
  // Create students
  Student student1 = Student('Alice');
  Student student2 = Student('Bob');
  Student student3 = Student('Charlie');
  
  // Static variable is shared and updated
  print('After creating students: ${Student.totalStudents}'); // After creating students: 3
  
  // Call static method
  Student.displaySchoolInfo();
  
  // Instance method can access static variables
  student1.displayInfo();
}

🔹 Static Methods

Static methods can be called without creating class instances:

class MathUtils {
  // Static constants
  static const double pi = 3.14159;
  static const double e = 2.71828;
  
  // Static methods for calculations
  static double circleArea(double radius) {
    return pi * radius * radius;
  }
  
  static double circleCircumference(double radius) {
    return 2 * pi * radius;
  }
  
  static double power(double base, int exponent) {
    double result = 1;
    for (int i = 0; i < exponent; i++) {
      result *= base;
    }
    return result;
  }
  
  static bool isPrime(int number) {
    if (number < 2) return false;
    for (int i = 2; i <= number ~/ 2; i++) {
      if (number % i == 0) return false;
    }
    return true;
  }
  
  // Static method to display all constants
  static void showConstants() {
    print('Mathematical Constants:');
    print('π (Pi) = $pi');
    print('e (Euler\'s number) = $e');
  }
}

void main() {
  // Use static methods without creating objects
  double radius = 5.0;
  
  print('Circle with radius $radius:');
  print('Area: ${MathUtils.circleArea(radius)}');
  print('Circumference: ${MathUtils.circleCircumference(radius)}');
  
  print('\nPower calculations:');
  print('2^3 = ${MathUtils.power(2, 3)}');
  print('5^2 = ${MathUtils.power(5, 2)}');
  
  print('\nPrime number check:');
  List numbers = [2, 4, 7, 9, 11];
  for (int num in numbers) {
    print('$num is prime: ${MathUtils.isPrime(num)}');
  }
  
  print('');
  MathUtils.showConstants();
}

🔹 Static vs Instance Members

Understanding the difference between static and instance members:

class BankAccount {
  // Static members (class-level)
  static String bankName = 'Global Bank';
  static double interestRate = 0.05;
  static int totalAccounts = 0;
  
  // Instance members (object-level)
  String accountHolder;
  double balance;
  int accountNumber;
  
  BankAccount(this.accountHolder, this.balance) {
    totalAccounts++;
    accountNumber = totalAccounts;
  }
  
  // Instance method - can access both static and instance members
  void displayAccountInfo() {
    print('--- Account Information ---');
    print('Bank: $bankName');                    // Static variable
    print('Account Holder: $accountHolder');     // Instance variable
    print('Account Number: $accountNumber');     // Instance variable
    print('Balance: \$${balance.toStringAsFixed(2)}');  // Instance variable
    print('Interest Rate: ${(interestRate * 100)}%');    // Static variable
  }
  
  // Static method - can only access static members
  static void displayBankInfo() {
    print('--- Bank Information ---');
    print('Bank Name: $bankName');
    print('Interest Rate: ${(interestRate * 100)}%');
    print('Total Accounts: $totalAccounts');
    // print('Balance: $balance');  // ERROR! Cannot access instance variable
  }
  
  // Instance method
  void deposit(double amount) {
    balance += amount;
    print('Deposited \$${amount.toStringAsFixed(2)}. New balance: \$${balance.toStringAsFixed(2)}');
  }
  
  // Static method to change interest rate for all accounts
  static void updateInterestRate(double newRate) {
    interestRate = newRate;
    print('Interest rate updated to ${(newRate * 100)}% for all accounts');
  }
}

void main() {
  // Access static members without creating objects
  print('Bank: ${BankAccount.bankName}');
  print('Current interest rate: ${(BankAccount.interestRate * 100)}%');
  
  // Create account objects
  BankAccount account1 = BankAccount('Alice', 1000.0);
  BankAccount account2 = BankAccount('Bob', 1500.0);
  
  // Display bank info (static method)
  BankAccount.displayBankInfo();
  
  print('');
  
  // Display individual account info (instance method)
  account1.displayAccountInfo();
  
  print('');
  
  // Update interest rate for all accounts (static method)
  BankAccount.updateInterestRate(0.06);
  
  // Both accounts now have the new interest rate
  account2.displayAccountInfo();
}