处理对象的多种状态及其相互转换——状态模式（三）

浅浅的花香味﹌ 2022-06-04 05:29 147阅读 0赞

## 3 完整解决方案 ##

Sunny软件公司开发人员使用状态模式来解决账户状态的转换问题，客户端只需要执行简单的存款和取款操作，系统根据余额将自动转换到相应的状态，其基本结构如图4所示：

![1358693610_6618.jpg][]

图4 银行账户结构图

在图4中，Account充当环境类角色，AccountState充当抽象状态角色，NormalState、OverdraftState和RestrictedState充当具体状态角色。完整代码如下所示：

//银行账户：环境类 
 class Account { 
 private AccountState state; //维持一个对抽象状态对象的引用 
 private String owner; //开户名 
 private double balance = 0; //账户余额 
 
 public Account(String owner,double init) { 
 this.owner = owner; 
 this.balance = balance; 
 this.state = new NormalState(this); //设置初始状态 
 System.out.println(this.owner + "开户，初始金额为" + init); 
 System.out.println("---------------------------------------------"); 
 } 
 
 public double getBalance() { 
 return this.balance; 
 } 
 
 public void setBalance(double balance) { 
 this.balance = balance; 
 } 
 
 public void setState(AccountState state) { 
 this.state = state; 
 } 
 
 public void deposit(double amount) { 
 System.out.println(this.owner + "存款" + amount); 
 state.deposit(amount); //调用状态对象的deposit()方法 
 System.out.println("现在余额为"+ this.balance); 
 System.out.println("现在帐户状态为"+ this.state.getClass().getName()); 
 System.out.println("---------------------------------------------"); 
 } 
 
 public void withdraw(double amount) { 
 System.out.println(this.owner + "取款" + amount); 
 state.withdraw(amount); //调用状态对象的withdraw()方法 
 System.out.println("现在余额为"+ this.balance); 
 System.out.println("现在帐户状态为"+ this. state.getClass().getName()); 
 System.out.println("---------------------------------------------"); 
 } 
 
 public void computeInterest() 
 { 
 state.computeInterest(); //调用状态对象的computeInterest()方法 
 } 
 } 
 
 //抽象状态类 
 abstract class AccountState { 
 protected Account acc; 
 public abstract void deposit(double amount); 
 public abstract void withdraw(double amount); 
 public abstract void computeInterest(); 
 public abstract void stateCheck(); 
 } 
 
 //正常状态：具体状态类 
 class NormalState extends AccountState { 
 public NormalState(Account acc) { 
 this.acc = acc; 
 } 
 
 public NormalState(AccountState state) { 
 this.acc = state.acc; 
 } 
 
 public void deposit(double amount) { 
 acc.setBalance(acc.getBalance() + amount); 
 stateCheck(); 
 } 
 
 public void withdraw(double amount) { 
 acc.setBalance(acc.getBalance() - amount); 
 stateCheck(); 
 } 
 
 public void computeInterest() 
 { 
 System.out.println("正常状态，无须支付利息！"); 
 } 
 
 //状态转换 
 public void stateCheck() { 
 if (acc.getBalance() > -2000 && acc.getBalance() <= 0) { 
 acc.setState(new OverdraftState(this)); 
 } 
 else if (acc.getBalance() == -2000) { 
 acc.setState(new RestrictedState(this)); 
 } 
 else if (acc.getBalance() < -2000) { 
 System.out.println("操作受限！"); 
 } 
 } 
 } 
 
 //透支状态：具体状态类 
 class OverdraftState extends AccountState 
 { 
 public OverdraftState(AccountState state) { 
 this.acc = state.acc; 
 } 
 
 public void deposit(double amount) { 
 acc.setBalance(acc.getBalance() + amount); 
 stateCheck(); 
 } 
 
 public void withdraw(double amount) { 
 acc.setBalance(acc.getBalance() - amount); 
 stateCheck(); 
 } 
 
 public void computeInterest() { 
 System.out.println("计算利息！"); 
 } 
 
 //状态转换 
 public void stateCheck() { 
 if (acc.getBalance() > 0) { 
 acc.setState(new NormalState(this)); 
 } 
 else if (acc.getBalance() == -2000) { 
 acc.setState(new RestrictedState(this)); 
 } 
 else if (acc.getBalance() < -2000) { 
 System.out.println("操作受限！"); 
 } 
 } 
 } 
 
 //受限状态：具体状态类 
 class RestrictedState extends AccountState { 
 public RestrictedState(AccountState state) { 
 this.acc = state.acc; 
 } 
 
 public void deposit(double amount) { 
 acc.setBalance(acc.getBalance() + amount); 
 stateCheck(); 
 } 
 
 public void withdraw(double amount) { 
 System.out.println("帐号受限，取款失败"); 
 } 
 
 public void computeInterest() { 
 System.out.println("计算利息！"); 
 } 
 
 //状态转换 
 public void stateCheck() { 
 if(acc.getBalance() > 0) { 
 acc.setState(new NormalState(this)); 
 } 
 else if(acc.getBalance() > -2000) { 
 acc.setState(new OverdraftState(this)); 
 } 
 } 
 }

编写如下客户端测试代码：

class Client {  
        public static void main(String args[]) {  
            Account acc = new Account("段誉",0.0);  
            acc.deposit(1000);  
            acc.withdraw(2000);  
            acc.deposit(3000);  
            acc.withdraw(4000);  
            acc.withdraw(1000);  
            acc.computeInterest();  
        }  
    }

编译并运行程序，输出结果如下：

<table style="border-collapse:collapse; border-spacing:0px; max-width:100%; background:rgb(242,242,242); color:rgb(69,69,69); font-family:&quot;PingFang SC&quot;,&quot;Microsoft YaHei&quot;,SimHei,Arial,SimSun; font-size:16px; width:503px; height:654px"> 
 <tbody style=""> 
 <tr style=""> 
 <td style=""> 段誉开户，初始金额为0.0 --------------------------------------------- 段誉存款1000.0 现在余额为1000.0 现在帐户状态为NormalState --------------------------------------------- 段誉取款2000.0 现在余额为-1000.0 现在帐户状态为OverdraftState --------------------------------------------- 段誉存款3000.0 现在余额为2000.0 现在帐户状态为NormalState --------------------------------------------- 段誉取款4000.0 现在余额为-2000.0 现在帐户状态为RestrictedState --------------------------------------------- 段誉取款1000.0 帐号受限，取款失败 现在余额为-2000.0 现在帐户状态为RestrictedState --------------------------------------------- 计算利息！ </td> 
 </tr> 
 </tbody> 
</table>

【作者：刘伟  [http://blog.csdn.net/lovelion][http_blog.csdn.net_lovelion] 】

[1358693610_6618.jpg]: https://img-my.csdn.net/uploads/201301/20/1358693610_6618.jpg
[http_blog.csdn.net_lovelion]: http://blog.csdn.net/lovelion