设计模式 - 行为型模式 - 状态模式

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//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));
        }
    }
}

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();
    }
}