展如下的BankAccount类新类CheckingAccount对每次存款和取款都收取1块钱的手续费。scalaclass BankAccountinitialBalance Double private var balance = initialBalance def depositamount Double = balance += amount; balance

class BankAccount(initialBalance: Double) {
  private var balance = initialBalance

  def deposit(amount: Double) = {
    balance += amount;
    balance
  }

  def withdraw(amount: Double) = {
    balance -= amount;
    balance
  }
}

class CheckingAccount(initialBalance: Double) extends BankAccount(initialBalance) {
  override def deposit(amount: Double): Double = {
    super.deposit(amount) - 1
  }

  override def withdraw(amount: Double): Double = {
    super.withdraw(amount) - 1
  }
}

在上述代码中，BankAccount类表示一个银行账户，CheckingAccount类是对BankAccount类的扩展，每次存款和取款都会收取1块钱的手续费。在CheckingAccount类中，通过使用super关键字调用BankAccount类的deposit和withdraw方法，并在其基础上减去1来实现手续费的收取