interface IApprovable {
  approve()
  reject()
}

interface IPayable {
  pay()
}

class Approvable implements IApprovable {
  ...
  approve() {...}
  reject() {...}
}

class NotApprovable implements IApprovable {
  ...
  approve() {...} <-- throw an error
  reject() {...} <-- throw an error
}

class Payable implements IPayable {
  ...
  pay() {...}
}

class NotPayable implements IPayable {
  ...
  pay() {...} <-- throw an error
}


class Transaction {
  private IApprovable approvable;
  private IPayable payable;

  Transaction(IApprovable approvable, IPayable payable) {
    this.approvable = approvable;
    this.payable = payable;
  }
}

public static main() {
  Transaction topup = new Transaction(new Approvable(), new Payable());
  Transaction transfer = new Transaction(new NotApprovable(), new NotPayable());
  Transaction refund = new Transaction(new Approvable(), new NotPayable());
}