状态模式

实验 22：状态模式

本次实验属于模仿型实验，通过本次实验学生将掌握以下内容：

1、理解状态模式的动机，掌握该模式的结构；

2、能够利用状态模式解决实际问题。

[实验任务]：银行账户
用Java代码模拟实现课堂上的“银行账户”的实例，要求编写客户端测试代码模拟用户存款和取款，注意账户对象状态和行为的变化。

源代码

public abstract class AccountState
{
 
    protected Account acc;
    protected double balance;
 
    public AccountState(Account acc, double balance)
    {
        super();
        this.acc = acc;
        this.balance = balance;
    }
 
    //检查账户状态
    public abstract void stateCheck();
 
    //存款
    public void deposit(double amount)
    {
        balance += amount;
        System.out.println("存款成功");
        System.out.println("当前余额为" + balance + "元");
    }
 
    //取款
    public void withdraw(double amount)
    {
        if ((balance - amount) > -1000)
        {
            System.out.println("取钱成功！");
            balance -= amount;
        } else
        {
            System.out.println("余额不足！");
        }
        System.out.println("当前余额：" + balance + "元");
    }
}
 
 
/**
 * 余额大于等于0
 * 绿色状态，正常状态，可存可取
 */
public class GreenState extends AccountState
{
    public GreenState(Account acc, double balance)
    {
        super(acc, balance);
    }
 
    @Override
    public void stateCheck()
    {
        if (balance < -1000)
        {
            acc.setState(new RedState(acc, balance));
        } else if (balance < 0 && balance >= -1000)
        {
            acc.setState(new YellowState(acc, balance));
        }
    }
}
 
/**
 * 余额小于-1000
 * 红色状态，透支状态，只能存不能取
 */
public class RedState extends AccountState
{
    public RedState(Account acc, double balance)
    {
        super(acc, balance);
    }
 
    @Override
    public void stateCheck()
    {
        if (balance >= -1000 && balance < 0)
        {
            acc.setState(new YellowState(acc, balance));
        } else if (balance >= 0)
        {
            acc.setState(new GreenState(acc, balance));
        }
    }
 
    //不能取款
    @Override
    public void withdraw(double amount)
    {
        System.out.println("余额不足！");
        System.out.println("当前余额：" + balance);
    }
}
 
/**
 * 余额小于0，并且大于等于-1000
 * 黄色状态，欠费状态，可存可取
 */
public class YellowState extends AccountState
{
    public YellowState(Account acc, double balance)
    {
        super(acc, balance);
    }
 
    @Override
    public void stateCheck()
    {
        if (balance >= 0)
        {
            acc.setState(new GreenState(acc, balance));
        } else if (balance < -1000)
        {
            acc.setState(new RedState(acc, balance));
        }
    }
}
 
 
/**
 * 账户类
 */
public class Account
{
    //账户状态
    private AccountState state;
    //账户所有人
    private String owner;
 
    public Account(String owner, double init)
    {
        this.owner = owner;
        this.state = new GreenState(this, init);
        this.state.stateCheck();
    }
 
    //设置状态
    public void setState(AccountState amount)
    {
        this.state = amount;
    }
 
    //存款
    public void deposit(double amount)
    {
        System.out.println(owner + "存" + amount + "元");
        state.deposit(amount);
        state.stateCheck();
    }
 
    //取款
    public void withdraw(double amount)
    {
        System.out.println(owner + "取" + amount + "元");
        state.withdraw(amount);
        state.stateCheck();
    }
}
 
 
public class Client
{
    public static void main(String[] args)
    {
        //初始化账户名和账户余额
        Account acc = new Account("账户：20213971 ", 200);
        //存入1000
        acc.deposit(1000);
        //取800
        acc.withdraw(800);
        //取1000
        acc.withdraw(1000);
        //取1000
        acc.withdraw(1000);
    }
}