定义和实现接口

代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            IBankAccount venusAccount = new SaverAccount();
            ITransferBankAccount jupiterAccount = new CurrentAccount();
            venusAccount.PayIn(200);
            jupiterAccount.PayIn(500);
            Console.WriteLine(jupiterAccount.TransferTo(venusAccount, 200).ToString());
            Console.WriteLine(venusAccount.ToString());
            Console.WriteLine(jupiterAccount.ToString());
            Console.ReadKey();
        }
    }

    #region 定义和实现接口
    public interface IBankAccount
    {
        void PayIn(decimal amount);
        bool Withdraw(decimal amount);
        decimal Balance
        {
            get;
        }
    }
    public interface ITransferBankAccount : IBankAccount
    {
        bool TransferTo(IBankAccount destination, decimal amount);
    }
    public class CurrentAccount : ITransferBankAccount
    {
        private decimal balance;
        //转账
        public bool TransferTo(IBankAccount destination, decimal amount)
        {
            bool result = false;
            result = Withdraw(amount);
            if (result)
            {
                destination.PayIn(amount);
            }
            return result;
        }
        //进账
        public void PayIn(decimal amount)
        {
            balance += amount;
        }
        //出账
        public bool Withdraw(decimal amount)
        {
            if (balance >= amount)
            {
                balance -= amount;
                return true;
            }
            Console.WriteLine("Withdrawal attempt failed.");
            return false;
        }

        public decimal Balance
        {
            get { return balance; }
        }
        public override string ToString()
        {
            return string.Format("Jupiter Blank Current Account:Balance={0,6:C}", balance);
        }
    }
    public class SaverAccount : IBankAccount
    {
        private decimal balance;
        public void PayIn(decimal amount)
        {
            balance += amount;
        }

        public bool Withdraw(decimal amount)
        {
            if (balance >= amount)
            {
                balance -= amount;
                return true;
            }
            Console.WriteLine("Withdrawal attempt failed.");
            return false;
        }

        public decimal Balance
        {
            get { return balance; }
        }
        public override string ToString()
        {
            return string.Format("Venus bank Saver:Balance={0,6:C}", balance);
        }
    }
    #endregion

}

结果：