第八章
1.这次把Account写成了抽象类，里面有几个虚抽象函数，在子类中实现了。
2.批量操作和统一接口，因为对象类型不一样，还要求统一实现，就用到虚函数，而函数接口设置为一样，在函数体额外加判断条件，来达到接口统一，更利于程序的封装性，安全性。
3.java里面的输出，也是调用类库，比如java.text.DecimalFormat可以控制输出小数点，java.io.IOException和java.util.*则是输入的专用库，每种类型的输入还不一样。
4.在Run里面定义输入变量cmd是char，cmd = (char)System.in.read()。 这时候可能发生异常所以有抛出声明throws IOException。
package ob5;
public class Date {
//日期类
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
public int[] DAYS_BEFORE_MONTH =new int[]{ 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 };
public void show(){
System.out.println( getYear()+"-"+getMonth()+"-"+getDay());
} //输出当前日期
public Date(int year, int month, int day){
this.year=year;
this.month=month;
this.day=day;
if (day <= 0 || day > getMaxDay()) {
System.out.println( "Invalid date: ");
show();
System.out.println();
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++;
}//用年、月、日构造日期
public int getYear() { return year; }
public int getMonth() { return month; }
public int getDay() { return day; }
public int getMaxDay(){
if (isLeapYear() && month == 2)
return 29;
else
return DAYS_BEFORE_MONTH[month]- DAYS_BEFORE_MONTH[month - 1];
} //获得当月有多少天
public boolean isLeapYear() { //判断当年是否为闰年
return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
}
//计算两个日期之间差多少天
public int distance(Date date) {
return totalDays - date.totalDays;
}
}
package ob5;
import java.text.DecimalFormat;
abstract public class Account {//账户类
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);
}
static DecimalFormat df = new DecimalFormat("0.0");//限制位数
public final String getId() { return id; }
public double getBalance() { return balance; }
public static double getTotal() { return total; }
//显示账户信息
abstract void deposit(final Date date, double amount,final String desc);
//取出现金，date为日期，amount为金额，desc为款项说明
abstract void withdraw(final Date date, double amount,final String desc);
//结算（计算利息、年费等），每月结算一次，date为结算日期
abstract void settle(final Date date);
//显示账户信息
public void show()
{
System.out.print(id + "\tBalance: " + df.format(balance));
}
}
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.print( "\t\tAvailable credit:" + getAvailableCredit());
}
}
package ob5;
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)
{
if(date.getMonth() == 1) {
double interest = acc.getSum(date) * rate / date.distance(new Date(date.getYear() - 1, 1, 1)); //计算年息
//计算年息
if (interest != 0)
record(date, interest, "interest");
acc.reset(date, getBalance());
}
}
}
package ob5;
public class Accumulator {//将某个数值按日累加
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;
}
}
package ob5;
import java.text.DecimalFormat;
import java.util.*;
import java.io.IOException;
public class Run {
public static void main(String[] args) throws IOException {
Date date = new Date(2008, 11, 1); //起始日期
//建立几个账户
SavingsAccount sa1 = new SavingsAccount(date, "S3755217", 0.015);
SavingsAccount sa2 = new SavingsAccount(date, "02342342", 0.015);
CreditAccount ca = new CreditAccount(date, "C5392394", 10000, 0.0005, 50);
Account accounts[] = { sa1, sa2, ca };
final int n = accounts.length; //账户总数
System.out.println("(d)deposit (w)withdraw (s)show (c)change day (n)next month (e)exit");
char cmd;
Scanner in=new Scanner(System.in); //使用Scanner类定义对象
int index, day;
double amount;
String desc;
DecimalFormat df = new DecimalFormat("0.0");
do {
//显示日期和总金额
date.show();
System.out.print("\tTotal: " + df.format(Account.getTotal()) + "\tcommand> ");
cmd = (char)System.in.read();
switch (cmd) {
case 'd': //存入现金
index = in.nextInt();
amount = in.nextDouble();
desc = in.nextLine();
accounts[index].deposit(date, amount, desc);
break;
case 'w': //取出现金
index = in.nextInt();
amount = in.nextDouble();
desc = in.nextLine();
accounts[index].withdraw(date, amount, desc);
break;
case 's': //查询各账户信息
for (int i = 0; i < n; i++) {
System.out.print("[" + i + "] ");
accounts[i].show();
System.out.println();
if(i<(n-1)) {System.in.read();}
}
break;
case 'c': //改变日期
day = in.nextInt();
if (day < date.getDay())
System.out.print("You cannot specify a previous day");
else if (day > date.getMaxDay())
System.out.print("Invalid day");
else
date = new Date(date.getYear(), date.getMonth(), day);
break;
case 'n': //进入下个月
if (date.getMonth() == 12)
date = new Date(date.getYear() + 1, 1, 1);
else
date = new Date(date.getYear(), date.getMonth() + 1, 1);
for (int i = 0; i < n; i++) {
accounts[i].settle(date);
if(i<(n-1)) {System.in.read();}
}
break;
}
} while (cmd != 'e');
in.close();
}
}
本文章为转载内容，我们尊重原作者对文章享有的著作权。如有内容错误或侵权问题，欢迎原作者联系我们进行内容更正或删除文章。
