To continue the conversation on inheritance, a subclass can provide its own custom implementation of a property or method that is inherited from a superclass. This is known as overriding.

To override a method, we can redeclare it in the subclass and add the override keyword to let the compiler know that we aren’t accidentally creating a method with the same name as the one in the parent class.

override func name(parameter) {

}

So here’s the BankAccount class again:

class BankAccount {

  var balance = 0.0

  func deposit(amount: Double) {
    balance += amount
  }

  func withdraw(amount: Double) {
    balance -= amount
  }

}

Suppose we want a new SavingsAccount class and we want to override the .withdraw() method from its superclass BankAccount:

class SavingsAccount: BankAccount {

  var interest = 0.0
  var numWithdraw = 0

  func addInterest() {
    let interest = balance * 0.01
    self.deposit(amount: interest)
  }

  override func withdraw(amount: Double) {
    balance -= amount
    numWithdraw += 1
  }

}

Here, the new .withdraw() method not only subtracts amount from balance, but it also increments numWithdraw.