participants
The classes and/or objects participating in this pattern are:
- Context (Account)
- defines the interface of interest to clients
- maintains an instance of a ConcreteState subclass that defines the current state.
- State (State)
- defines an interface for encapsulating the behavior associated with a particular state of the Context.
- Concrete State (RedState, SilverState, GoldState)
- each subclass implements a behavior associated with a state of Context
模拟一个借记卡的例子，假设每次存款都有利息，并且不允许透支
using System;
using System.Collections.Generic; using System.Linq; using System.Text;namespace State
{ class Program { static void Main(string[] args) { Account account = new Account("张三丰"); account.Deposit(500.0); account.Deposit(5000.0); account.Withdraw(5499); Console.ReadKey(); } }abstract class State
{protected Account account;
protected double balance; protected double interest; protected double lowerLimit; protected double upperLimit;public Account Account
{get { return account; }
set { account = value; }
}
//余款 public double Balance {get { return balance; }
set { balance = value; }
}
public abstract void Deposit(double amount);
public abstract void Withdraw(double amount);
public abstract void PayInterest();
}
class RedState : State
{private double _serviceFee;
public RedState(State state)
{this.balance = state.Balance;
this.account = state.Account;
Initialize();
}
private void Initialize()
{// 正式应用时取自数据源或配置文件
interest = 0.0;
lowerLimit = -100.0; upperLimit = 0.0; _serviceFee = 15.00;}
//存款 public override void Deposit(double amount) {balance += amount;
StateChangeCheck();
PayInterest(); }
public override void Withdraw(double amount)
{amount = amount - _serviceFee;
Console.WriteLine("已透支，无法取款！");
}
public override void PayInterest()
{// 没有利息
}
private void StateChangeCheck()
{if (balance > upperLimit)
{account.State = new SilverState(this);
}
}
}
class SilverState : State
{public SilverState(State state) :
this(state.Balance, state.Account)
{}
public SilverState(double balance, Account account)
{this.balance = balance;
this.account = account;
Initialize();
}
private void Initialize()
{interest = 0.02;
lowerLimit = 0.0; upperLimit = 1000.0; }
public override void Deposit(double amount)
{balance += amount;
StateChangeCheck(); PayInterest(); }
public override void Withdraw(double amount)
{double tempBalance = balance - amount;
if (tempBalance > 0) { balance -= amount; } else { Console.WriteLine("已透支，无法取款！"); } StateChangeCheck();}
public override void PayInterest()
{Console.WriteLine("利息= {0:C}", interest * balance);
balance += interest * balance; StateChangeCheck(); }
private void StateChangeCheck()
{if (balance < lowerLimit)
{account.State = new RedState(this);
}
else if (balance > upperLimit)
{account.State = new GoldState(this);
}
}
}
class GoldState : State
{// Overloaded constructors
public GoldState(State state)
: this(state.Balance, state.Account)
{}
public GoldState(double balance, Account account)
{this.balance = balance;
this.account = account;
Initialize();
}
private void Initialize()
{interest = 0.05;
lowerLimit = 1000.0; upperLimit = 10000.0; }
public override void Deposit(double amount)
{balance += amount;
StateChangeCheck();
PayInterest(); }
public override void Withdraw(double amount)
{ double tempBalance = balance - amount; if (tempBalance > 0) { balance -= amount; } else { Console.WriteLine("已透支，无法取款！"); }StateChangeCheck();
}
public override void PayInterest()
{ Console.WriteLine("利息= {0:C}", interest * balance); balance += interest * balance; StateChangeCheck();}
private void StateChangeCheck()
{if (balance < 0.0)
{account.State = new RedState(this);
}
else if (balance < lowerLimit)
{account.State = new SilverState(this);
}
}
}
class Account
{private State _state;
private string _owner;
// Constructor
public Account(string owner)
{// New accounts are 'Silver' by default
this._owner = owner;
this._state = new SilverState(0.0, this);
}
// Properties
public double Balance
{get { return _state.Balance; }
}
public State State
{get { return _state; }
set { _state = value; }
}
public void Deposit(double amount)
{_state.Deposit(amount);
Console.WriteLine("存款 {0:C} --- ", amount);
Console.WriteLine(" 余额 = {0:C}", this.Balance);
Console.WriteLine(" 状态 = {0}",
this.State.GetType().Name);
Console.WriteLine("");
}
public void Withdraw(double amount)
{_state.Withdraw(amount);
Console.WriteLine("取款 {0:C} --- ", amount);
Console.WriteLine(" 余额 = {0:C}", this.Balance);
Console.WriteLine(" 状态 = {0}\n",
this.State.GetType().Name);
}
} }