State Pattern Code Review

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Download Description:state pattern download
.NETFramework:3.5
.NET Language:C#
Date Published:2009-07-01
Download Size:9 KB

Define the Pattern Interface and Handler Objects

Define the IState interface to be used as the "blueprint" for the main State classes.

interface IState { void Deposit(Context context, Double amount); Boolean Withdraw(Context context, Double amount); Boolean PayInterest(Context context); }

The RedState class (object) represents one particular state.

class RedState : IState { public void Deposit(Context context, double amount) { context.Balance += amount;
if (context.Balance > 0) { context.State = new SliverState(); } } public Boolean Withdraw(Context context, double amount) { context.Balance -= 15.00; Console.WriteLine("No funds available for withdrawal!\n"); return (false); } public Boolean PayInterest(Context context) { Console.WriteLine("No interest paid!\n"); return (false); } }

The SliverState class (object) represents another available state, and is able to update the State object as required.

class SliverState : IState { public void Deposit(Context context, double amount) { context.Balance += amount; UpdateState(context); } public Boolean Withdraw(Context context, double amount) { context.Balance -= amount; UpdateState(context); return (true); } public Boolean PayInterest(Context context) { Console.WriteLine("No interest paid!\n"); return (false); } private void UpdateState(Context context) { if (context.Balance < 0) { context.State = new RedState(); } else if (context.Balance > 1000) { context.State = new GoldState(); } } }

The GoldState class (object) represents another available state, and is able to update the State object as required.

class GoldState : IState { public void Deposit(Context context, double amount) { context.Balance += amount; UpdateState(context); } public Boolean Withdraw(Context context, double amount) { context.Balance -= amount; UpdateState(context); return (true); } public Boolean PayInterest(Context context) { context.Balance *= 1.05; UpdateState(context); return (true); } private void UpdateState(Context context) { if (context.Balance < 0) { context.State = new RedState(); } else if (context.Balance < 1000) { context.State = new SliverState(); } } }

Define the Context Object

The Context class (object) initialises the State object and invokes methods on the State class (object).

class Context { public IState State { get; set; } public Double Balance { get; set; }
private String m_owner;
public Context(String Owner) { this.m_owner = Owner; this.State = new SliverState(); }
public void Deposit(Double amount) { State.Deposit(this, amount); Console.WriteLine(String.Format("Deposited {0:C}", amount)); this.ShowBalance(); } public void Withdraw(Double amount) { if (State.Withdraw(this, amount)) { Console.WriteLine(String.Format("Withdrew {0:C}", amount)); } else { Console.WriteLine("\t15% charge applied"); } this.ShowBalance(); } public void PayInterest() { if (State.PayInterest(this)) { Console.WriteLine("Interested Paid"); this.ShowBalance(); } } private void ShowBalance() { Console.WriteLine(String.Format("\tBalance {0:C}", this.Balance)); Console.WriteLine(String.Format("\tStatus {0}\n", this.State.GetType().Name)); } }

Use the State Pattern

The Program class creates the Context object invokes methods on the Context class (object).

class Program { static void Main(string[] args) { Context context = new Context("Jim Johnson");
context.Deposit(500.00); context.PayInterest(); context.Deposit(300.00); context.Deposit(550.00); context.PayInterest(); context.Withdraw(2000.00); context.Withdraw(1100.00);
Console.Read(); } }