个人银行账户管理系统（c++改写java）第7章：继承与派生，抽象出父类，增添子类

public class Account {
    private String id;    //帐号
    private double balance;    //余额
    private static double total = 0; //所有账户的总金额
    
        //供派生类调用的构造函数，id为账户
    protected Account(final Date date, final String id)
    {
        this.id=id;
        balance=0;
        date.show();
        System.out.println("\t#" + id + " created");
    }
        //记录一笔帐，date为日期，amount为金额，desc为说明
    protected void record(final Date date, double amount, final String desc)
    {
        amount = Math.floor(amount * 100 + 0.5) / 100;    //保留小数点后两位
        balance += amount;
        total += amount;
        date.show();
        System.out.println( "\t#" + id + "\t" + amount + "\t" + balance + "\t" + desc );
    }
        //报告错误信息
    protected void error(final String msg)
    {
        System.out.println("Error(#" + id + "):" + msg);
    }
    
    public final String getId() { return id; }
    public double getBalance() { return balance; }
    public static double getTotal() { return total; }
        //显示账户信息
    public void show()
    {
        System.out.print(id + "\tBalance: " + balance);//这里不用println
    }
}

public class CreditAccount extends Account{//信用账户类

    private Accumulator acc;    //辅助计算利息的累加器
    private double credit;        //信用额度
    private double rate;        //欠款的日利率
    private double fee;            //信用卡年费

    private double getDebt() {    //获得欠款额
            double balance = getBalance();
            return (balance < 0 ? balance : 0);
    }
    
        //构造函数
    public CreditAccount(final Date date,final String id, double credit, double rate, double fee)
    {
        super(date, id);
        this.credit=credit;
        this.rate=rate;
        this.fee=fee;
        acc = new Accumulator(date, 0);
        
    }
    public double getCredit() { return credit; }
    public double getRate() { return rate; }
    public double getFee() { return fee; }
    public double getAvailableCredit() {    //获得可用信用
            if (getBalance() < 0) 
                return credit + getBalance();
            else
                return credit;
        }
        //存入现金
    public void deposit(final Date date, double amount,final String desc)
    {
        record(date, amount, desc);
        acc.change(date, getDebt());
    }
        //取出现金
    public void withdraw(final Date date, double amount,final String desc)
    {
        if (amount - getBalance() > credit) {
            error("not enough credit");
        } else {
            record(date, -amount, desc);
            acc.change(date, getDebt());
        }
    }
        //结算利息和年费，每月1日调用一次该函数
    public void settle(final Date date)
    {
        double interest = acc.getSum(date) * rate;
        if (interest != 0)
            record(date, interest, "interest");
        if (date.getMonth() == 1)
            record(date, -fee, "annual fee");
        acc.reset(date, getDebt());
    }
    public void show()
    {
        super.show();
        System.out.println( "\tAvailable credit:" + getAvailableCredit());
    }
}

public class SavingsAccount extends Account {//储蓄账户类

    private Accumulator acc;    //辅助计算利息的累加器
    private double rate;        //存款的年利率
    
        //构造函数
    public SavingsAccount(final Date date,final String id, double rate)
    {
        super(date,id);
        this.rate = rate;
        acc=new Accumulator(date,0);
    }
    public double getRate() { return rate; }
        //存入现金
    public void deposit(final Date date, double amount,final String desc)
    {
        record(date, amount, desc);
        acc.change(date, getBalance());
    }
        //取出现金
    public void withdraw(final Date date, double amount,final String desc)
    {
        if (amount > getBalance()) {
            error("not enough money");
        } else {
            record(date, -amount, desc);
            acc.change(date, getBalance());
        }
    }
        //结算利息，每年1月1日调用一次该函数
    public void settle(final Date date)
    {
        double interest = acc.getSum(date) * rate / date.distance(new Date(date.getYear() - 1, 1, 1));    //计算年息
        if (interest != 0)
            record(date, interest, "interest");
        acc.reset(date, getBalance());
    }
}

public class Accumulator {
    private Date lastDate;    //上次变更数值的时期
    private double value;    //数值的当前值
    private double sum;        //数值按日累加之和
    
        //构造函数，date为开始累加的日期，value为初始值
    public Accumulator(final Date date, double value)
    {
        lastDate=date;
        this.value=value;
        sum=0;
    }
        //获得到日期date的累加结果
    public double getSum(final Date date){
            return sum + value * date.distance(lastDate);
        }

        //在date将数值变更为value
    public void change(final Date date, double value) {
            sum = getSum(date);
            lastDate = date;
            this.value = value;
        }

        //初始化，将日期变为date，数值变为value，累加器清零
    public void reset(final  Date date, double value) {
            lastDate = date;
            this.value = value;
            sum = 0;
        }
}

public class Date {
    //存储平年中某个月1日之前有多少天，为便于getMaxDay函数的实现，该数组多出一项
            final int DAYS_BEFORE_MONTH[] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 };
            private int year;        //年
            private int month;        //月
            private int day;        //日
            private int totalDays;    //该日期是从公元元年1月1日开始的第几天

            boolean isLeapYear() {    //判断当年是否为闰年
                return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
            }
            public Date(int year, int month, int day)    //用年、月、日构造日期
            {
                this.day = day;
                this.month = month;
                this.year = year;
                if (day <= 0 || day > getMaxDay()) {
                    System.out.println("Invalid date: ");
                    show();
                    System.exit(1);
                }
                int years = year - 1;
                totalDays = years * 365 + years / 4 - years / 100 + years / 400 + DAYS_BEFORE_MONTH[month - 1] + day;
                if (isLeapYear() && month > 2) totalDays++;
            }
            public int getYear() { return year; }
            public int getMonth() { return month; }
            public int getDay() { return day; }
            public int getMaxDay()        //获得当月有多少天
            {
                if (isLeapYear() && month == 2)
                    return 29;
                else
                    return DAYS_BEFORE_MONTH[month]- DAYS_BEFORE_MONTH[month - 1];
            }
                
            public void show()            //输出当前日期
            {
                System.out.print(getYear() + "-" + getMonth() + "-" + getDay());
            }
                //计算两个日期之间差多少天    
            int distance(Date date)
            {
                return totalDays - date.totalDays;
            }
}

public class main {
    public static void main(String[] args) {
        Date date = new Date(2008, 11, 1);    //起始日期
        //建立几个账户
        SavingsAccount sa1 = new SavingsAccount(date, "AAAAA", 0.015);
        sa1.deposit(new Date(2008, 11, 5), 5000, "salary");
        sa1.withdraw(new Date(2008, 12, 5), 500, "happy");
        sa1.settle(new Date(2009, 1, 1));
        sa1.show();
        System.out.println();
        SavingsAccount sa2 = new SavingsAccount(date, "02342342", 0.015);
        CreditAccount ca = new CreditAccount(date, "BBBBB", 10000, 0.0005, 50);
        //11月份的几笔账目
        ca.withdraw(new Date(2008, 11, 15), 2000, "buy a cell");
        sa2.deposit(new Date(2008, 11, 25), 10000, "sell stock 0323");
        //结算信用卡
        ca.show();
        ca.withdraw(new Date(2008, 12, 1), 52000, "buy a car");
        ca.settle(new Date(2008, 12, 30));
        ca.settle(new Date(2008, 12, 31));
        ca.settle(new Date(2009, 1, 1));
        //12月份的几笔账目
        ca.show();
        ca.deposit(new Date(2008, 12, 31), 2016, "repay the credit");
        //结算所有账户
        sa2.settle(new Date(2009, 1, 1));
        ca.settle(new Date(2009, 1, 1));
        //输出各个账户信息
        sa2.show();
        System.out.println();
        ca.show();
        System.out.println( "Total: " + Account.getTotal());
    }
}

由Account派生出两个子类：SavingsAccount类和CreditAccount类，语法上与c++差别不大。