Java教程
第7周大作业 C++改Java——个人银行账户管理系统
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共6次改写
一，4_9: 第四章——类
package java4_9;
//储蓄账户类
class SavingsAccount{
private int id,lastDate; //账号 上次变更余额的时期
private double balance,rate,accumulation; //余额 存款的年利率 余额按日累加之和
//构造函数
public SavingsAccount(int date, int id, double rate){
this.id = id;
this.balance = 0;
this.rate = rate;
this.lastDate = date;
this.accumulation = 0;
System.out.println( date+"\t#"+ id +" is created" );
}
//记录一笔帐，date为日期，amount为金额，desc为说明
private void record(int date, double amount){
accumulation = accumulate(date);
lastDate = date;
balance += amount;
System.out.println( date + " #" + id + " " + String.format("%.2f", amount)
+ " "+ String.format("%.2f", balance) );
}
//获得到指定日期为止的存款金额按日累积值
private double accumulate(int date){
return accumulation + balance * (date - lastDate);
}
public int getId() { return id; }
public double getBalance() { return balance; }
public double getRate() { return rate; }
//存入现金
public void deposit(int date, double amount){
record(date, amount);
}
//取出现金
public void withdraw(int date, double amount){
if (amount > getBalance())
System.out.println( "Error: not enough money" );
else
record(date, -amount);
}
//结算利息，每年1月1日调用一次该函数
public void settle(int date){
double interest = accumulate(date) * rate / 365; //计算年息
if (interest != 0)
record(date, interest);
accumulation = 0;
}
//显示账户信息
public void show(){
System.out.println( "#" + id + "\tBalance: " + balance );
}
}
public class java4_9 {
public static void main(String[] args)
{
// TODO Auto-generated method stub
//建立几个账户
SavingsAccount sa0 = new SavingsAccount(1, 21325302, 0.015);
SavingsAccount sa1 = new SavingsAccount(1, 58320212, 0.015);
//几笔账目
sa0.deposit(5, 5000);
sa1.deposit(25, 10000);
sa0.deposit(45, 5500);
sa1.withdraw(60, 4000);
//开户后第90天到了银行的计息日，结算所有账户的年息
sa0.settle(90);
sa1.settle(90);
//输出各个账户信息
sa0.show();
sa1.show();
}
}
二，5_11:第五章——增添静态属性与方法
增加静态的属性total，方便记录所有账号的总金额，同时静态方法，方便查询total.
静态方法可以直接通过"类名.方法"的形式进行方法调用。
package java5_11;
//储蓄账户类
class SavingsAccount{
private int id,lastDate; //账号 上次变更余额的时期
private double balance,rate,accumulation; //余额 存款的年利率 余额按日累加之和
private static double total=0; //所有账户的总金额
//构造函数
public SavingsAccount(int date, int id, double rate){
this.id = id;
this.balance = 0;
this.rate = rate;
this.lastDate = date;
this.accumulation = 0;
System.out.println( date+"\t#"+ id +" is created" );
}
//记录一笔帐，date为日期，amount为金额，desc为说明
private void record(int date, double amount){
accumulation = accumulate(date);
lastDate = date;
balance += amount;
total += amount;
System.out.println( date + " #" + id + " " + String.format("%.2f", amount)
+ " "+ String.format("%.2f", balance) );
}
//获得到指定日期为止的存款金额按日累积值
private double accumulate(int date){
return accumulation + balance * (date - lastDate);
}
public int getId() { return id; }
public double getBalance() { return balance; }
public double getRate() { return rate; }
public static double getTotal() { return total; }
//存入现金
public void deposit(int date, double amount){
record(date, amount);
}
//取出现金
public void withdraw(int date, double amount){
if (amount > getBalance())
System.out.println( "Error: not enough money" );
else
record(date, -amount);
}
//结算利息，每年1月1日调用一次该函数
public void settle(int date){
double interest = accumulate(date) * rate / 365; //计算年息
if (interest != 0)
record(date, interest);
accumulation = 0;
}
//显示账户信息
public void show(){
System.out.println( "#" + id + "\tBalance: " + balance );
}
}
public class java5_11 {
public static void main(String[] args){
//建立几个账户
SavingsAccount sa0 = new SavingsAccount(1, 21325302, 0.015);
SavingsAccount sa1 = new SavingsAccount(1, 58320212, 0.015);
//几笔账目
sa0.deposit(5, 5000);
sa1.deposit(25, 10000);
sa0.deposit(45, 5500);
sa1.withdraw(60, 4000);
//开户后第90天到了银行的计息日，结算所有账户的年息
sa0.settle(90);
sa1.settle(90);
//输出各个账户信息
sa0.show();System.out.println();
sa1.show();System.out.println();
System.out.println( "Total: " + SavingsAccount.getTotal() );
}
}
三，6_25:第六章——使用了对象数组，增添了字符串，多出一个类Date
Date.java
package java6_25;
public class Date{ //日期类
public final int[] DAYS_BEFORE_MONTH = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 };
private int year,month,day,totalDays; //年 月 日 该日期是从公元元年1月1日开始的第几天
//用年、月、日构造日期
public Date(int year, int month, int day){
this.year=year;
this.month=month;
this.day=day;
if (day <= 0 || day > getMaxDay()) {
System.out.print( "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++;
}
public final int getYear() { return year; }
public final int getMonth() { return month; }
public final int getDay() { return day; }
//获得当月有多少天
public final int getMaxDay(){
if (isLeapYear() && month == 2)
return 29;
else
return DAYS_BEFORE_MONTH[month]- DAYS_BEFORE_MONTH[month - 1];
}
//判断当年是否为闰年
public final boolean isLeapYear() {
return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
}
//输出当前日期
public final void show(){
System.out.print(getYear()+"-"+getMonth()+"-"+ getDay());
}
//计算两个日期之间差多少天
public final int distance(final Date date) {
return totalDays - date.totalDays;
}
}
java6_25.java
package java6_25;
class SavingsAccount{
private String id; //账号
private Date lastDate; // 上次变更余额的时期
private double balance,rate,accumulation; //余额 存款的年利率 余额按日累加之和
private static double total=0; //所有账户的总金额
//构造函数
public SavingsAccount(final Date date, final String id, double rate){
this.id = id;
this.balance = 0;
this.rate = rate;
this.lastDate = date;
this.accumulation = 0;
date.show();
System.out.println("\t#"+id+" is created");
}
//记录一笔帐，date为日期，amount为金额，desc为说明
private void record(final Date date, double amount, final String desc){
accumulation = accumulate(date);
lastDate = date;
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);
}
//获得到指定日期为止的存款金额按日累积值
private double accumulate(final Date date){
return accumulation + balance * date.distance(lastDate);
}
//报告错误信息
public final void error(final String msg)
{
System.out.println("Error(#" + id +"): " + msg );
}
public final String getId() { return id; }
public final double getBalance() { return balance; }
public final double getRate() { return rate; }
public static double getTotal() { return total; }
//存入现金
public void deposit(final Date date, double amount, final String desc){
record(date, amount, desc);
}
//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);
}
//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 = accumulate(date) * rate //计算年息
/ date.distance(new Date(date.getYear() - 1, 1, 1));
if (interest != 0)
record(date, interest, "interest");
accumulation = 0;
}
//显示账户信息
public final void show(){
System.out.print(id+"\tBalance: "+balance);
}
}
public class java6_25 {
public static void main(String[] args) {
Date date = new Date(2008, 11, 1); //起始日期
//建立几个账户
SavingsAccount[] accounts= {
new SavingsAccount(date, "S3755217", 0.015),
new SavingsAccount(date, "02342342", 0.015)
};
final int n = accounts.length; // => sizeof(accounts) / sizeof(SavingsAccount); 账户总数
//11月份的几笔账目
accounts[0].deposit(new Date(2008, 11, 5), 5000, "salary");
accounts[1].deposit(new Date(2008, 11, 25), 10000, "sell stock 0323");
//12月份的几笔账目
accounts[0].deposit(new Date(2008, 12, 5), 5500, "salary");
accounts[1].withdraw(new Date(2008, 12, 20), 4000, "buy a laptop");
//结算所有账户并输出各个账户信息
System.out.println();
for (int i = 0; i < n; i++) {
accounts[i].settle(new Date(2009, 1, 1));
accounts[i].show();
System.out.println();
}
System.out.println( "Total: "+ SavingsAccount.getTotal() );
}
}
四，7_10:第七章——多了一个类Accumulator及用了类的继承
抽象出了父类使得代码扩展性更高，父类Account，派生出子类creditAccount和savingsaccount。
继承写法：
class CreditAccount extends Account
class SavingsAccount extends Account
主函数：account7.java
package java7_10;
//账户类
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;
this.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 final 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);
}
}
//储蓄账户类
class SavingsAccount extends Account {
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);
//若一个父类只要有一个带参数的构造方法，
// 那么在写其子类的构造方法时必须先通过super调用父类的构造方法而且super只能写在子类构造方法体内的第一行。
this.rate=rate;
acc=new Accumulator(date,0);
}
public final 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 //计算年息
/ date.distance(new Date(date.getYear() - 1, 1, 1));
if (interest != 0)
record(date, interest, "interest");
acc.reset(date, getBalance());
}
}
//信用账户类
class CreditAccount extends Account {
private Accumulator acc; //辅助计算利息的累加器
private double credit,rate,fee; //信用额度 欠款的日利率 信用卡年费
//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);
}
//获得欠款额
private final double getDebt() {
double balance = getBalance();
return (balance < 0 ? balance : 0);
}
public final double getCredit() { return credit; }
public final double getRate() { return rate; }
public final double getFee() { return fee; }
//获得可用信用
public final double getAvailableCredit() {
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 final void show() {
super.show();
System.out.print("\tAvailable credit:" + getAvailableCredit());
}
}
public class account7 {
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, "S3755217", 0.015);
SavingsAccount sa2=new SavingsAccount(date, "02342342", 0.015);
CreditAccount ca=new CreditAccount(date, "C5392394", 10000, 0.0005, 50);
//11月份的几笔账目
sa1.deposit(new Date(2008, 11, 5), 5000, "salary");
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.settle(new Date(2008, 12, 1));
//12月份的几笔账目
ca.deposit(new Date(2008, 12, 1), 2016, "repay the credit");
sa1.deposit(new Date(2008, 12, 5), 5500, "salary");
//结算所有账户
sa1.settle(new Date(2009, 1, 1));
sa2.settle(new Date(2009, 1, 1));
ca.settle(new Date(2009, 1, 1));
//输出各个账户信息
System.out.println();
sa1.show(); System.out.println();
sa2.show(); System.out.println();
ca.show(); System.out.println();
System.out.println( "Total: " + Account.getTotal() );
}
}
Accumulator.java
package java7_10;
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,sum; //数值的当前值 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)
{
this.lastDate=date;
this.value=value;
this.sum=0;
}
//获得到日期date的累加结果
public final 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;
}
}
Date.java
package java7_10;
public class Date{ //日期类
public final int[] DAYS_BEFORE_MONTH = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 };
private int year,month,day,totalDays; //年 月 日 该日期是从公元元年1月1日开始的第几天
//用年、月、日构造日期
public Date(int year, int month, int day)
{
this.year=year;
this.month=month;
this.day=day;
if (day <= 0 || day > getMaxDay()) {
System.out.print( "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++;
}
public final int getYear() { return year; }
public final int getMonth() { return month; }
public final int getDay() { return day; }
//获得当月有多少天
public final int getMaxDay()
{
if (isLeapYear() && month == 2)
return 29;
else
return DAYS_BEFORE_MONTH[month]- DAYS_BEFORE_MONTH[month - 1];
}
//判断当年是否为闰年
public final boolean isLeapYear()
{
return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
}
//输出当前日期
public final void show()
{
System.out.print(getYear()+"-"+getMonth()+"-"+ getDay());
}
//计算两个日期之间差多少天
public final int distance(final Date date)
{
return totalDays - date.totalDays;
}
}
五，8_8:第八章——用了多态
java里的多态主要体现在重载和覆盖，注意java里没有运算符的重载。类似c++里的虚函数，java里面有abstract关键字，只要某给个类里含有abstract方法，就必须在类前声明abstract。
主函数：account8.java
package java8_8;
import java.util.Scanner;
//账户类
abstract 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;
this.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 final double getBalance() { return balance; }
public static double getTotal() { return total; }
//存入现金，date为日期，amount为金额，desc为款项说明
public 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
public 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
public abstract void settle(final Date date);
//显示账户信息
public void show(){
System.out.println(id + "\tBalance: " + balance);
}
}
//储蓄账户类
class SavingsAccount extends Account {
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);
//若一个父类只要有一个带参数的构造方法，
// 那么在写其子类的构造方法时必须先通过super调用父类的构造方法而且super只能写在子类构造方法体内的第一行。
this.rate=rate;
acc=new Accumulator(date,0);
}
public final 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 //计算年息
/ date.operator(new Date(date.getYear() - 1, 1, 1));
if (interest != 0)
record(date, interest, "interest");
acc.reset(date, getBalance());
}
}
//信用账户类
class CreditAccount extends Account {
private Accumulator acc; //辅助计算利息的累加器
private double credit,rate,fee; //信用额度 欠款的日利率 信用卡年费
//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);
}
//获得欠款额
private final double getDebt() {
double balance = getBalance();
return (balance < 0 ? balance : 0);
}
public final double getCredit() { return credit; }
public final double getRate() { return rate; }
public final double getFee() { return fee; }
//获得可用信用
public final double getAvailableCredit() {
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 final void show() {
super.show();
System.out.println( "\tAvailable credit:" + getAvailableCredit() );
}
}
public class account8 {
public static void main(String[] args) {
// TODO Auto-generated method stub
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;// => sizeof(accounts) / sizeof(SavingsAccount); 账户总数
System.out.println( "(d)deposit (w)withdraw (s)show (c)change day (n)next month (e)exit" );
char cmd;
do {
//显示日期和总金额
date.show();
System.out.println( "\tTotal: " +Account.getTotal() + "\tcommand> " );
int index, day;
double amount;
String desc;
@SuppressWarnings("resource")
Scanner input=new Scanner(System.in);
String c=input.next();
cmd=c.charAt(0);
switch (cmd) {
case 'd': //存入现金
index=input.nextInt();
amount=input.nextDouble();
desc=input.next();
accounts[index].deposit(date, amount, desc);
break;
case 'w': //取出现金
index=input.nextInt();
amount=input.nextDouble();
desc=input.next();
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();
}
break;
case 'c': //改变日期
day=input.nextInt();
if (day < date.getDay())
System.out.println( "You cannot specify a previous day" );
else if (day > date.getMaxDay())
System.out.println( "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);
break;
}
} while (cmd != 'e');
}
}
Accumulator.java
package java8_8;
//将某个数值按日累加
public class Accumulator {
private Date lastDate; //上次变更数值的时期
private double value,sum; //数值的当前值 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){
this.lastDate=date;
this.value=value;
this.sum=0;
}
//获得到日期date的累加结果
public final double getSum(final Date date) {
return sum + value * (date.operator(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;
}
}
Date.java
package java8_8;
//日期类
public class Date{
public final int[] DAYS_BEFORE_MONTH = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 };
private int year,month,day,totalDays; //年 月 日 该日期是从公元元年1月1日开始的第几天
//用年、月、日构造日期
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("\n");
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 final int getYear() { return year; }
public final int getMonth() { return month; }
public final int getDay() { return day; }
//获得当月有多少天
public final int getMaxDay(){
if (isLeapYear() && month == 2)
return 29;
else
return DAYS_BEFORE_MONTH[month]- DAYS_BEFORE_MONTH[month - 1];
}
//判断当年是否为闰年
public final boolean isLeapYear() {
return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
}
//输出当前日期
public final void show(){
System.out.println( getYear() + "-" + getMonth() + "-" + getDay() );
}
//计算两个日期之间差多少天
public final int operator (final Date date) {
return totalDays - date.totalDays;
}
}
九，9_16:第九章——使用了容器来代替数组
注意到java中没有指针和模板，同时java里也没有char。
输入字符串，然后通过charAt（0）取出第一个字符。
主函数：account9.java
package java9_16;
import java.util.ArrayList;
//import java.util.Arrays;
//import java.util.*;
import java.util.Scanner;
//账户类
abstract 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;
this.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 + "\n");
}
public final String getId() { return id; }
public final double getBalance() { return balance; }
public static double getTotal() { return total; }
//存入现金，date为日期，amount为金额，desc为款项说明
public 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
public 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
public abstract void settle(final Date date);
//显示账户信息
public void show(){
System.out.println( id + "\tBalance: " + balance );
}
}
//储蓄账户类
class SavingsAccount extends Account {
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);
//若一个父类只要有一个带参数的构造方法，
// 那么在写其子类的构造方法时必须先通过super调用父类的构造方法才能完成子类的构造方法而且super只能写在子类构造方法体内的第一行。
this.rate=rate;
acc=new Accumulator(date,0);
}
public final 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 //计算年息
/ date.operator(new Date(date.getYear() - 1, 1, 1));
if (interest != 0)
record(date, interest, "interest");
acc.reset(date, getBalance());
}
}
//信用账户类
class CreditAccount extends Account {
private Accumulator acc; //辅助计算利息的累加器
private double credit,rate,fee; //信用额度 欠款的日利率 信用卡年费
//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);
}
//获得欠款额
private final double getDebt() {
double balance = getBalance();
return (balance < 0 ? balance : 0);
}
public final double getCredit() { return credit; }
public final double getRate() { return rate; }
public final double getFee() { return fee; }
//获得可用信用
public final double getAvailableCredit() {
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 final void show() {
super.show();
System.out.println( "\tAvailable credit:" + getAvailableCredit() );
}
}
public class account9 {
public static void main(String[] args) {
Date date=new Date(2008, 11, 1); //起始日期
//Array<Account *> accounts(0); 创建账户数组，元素个数为0
ArrayList<Account> accounts = new ArrayList<>();
System.out.println("(a)add account (d)deposit (w)withdraw (s)show (c)change day (n)next month (e)exit" );
char cmd;
do {
//显示日期和总金额
date.show();
System.out.println("\tTotal: " +Account.getTotal() + "\tcommand> ");
char type;
int index, day;
double amount, credit, rate, fee;
String id, desc;
Account account;
@SuppressWarnings("resource")
Scanner input=new Scanner(System.in);
String c=input.next();
cmd=c.charAt(0);
switch (cmd) {
case 'a': //增加账户
Scanner inputt=new Scanner(System.in);
String t=inputt.next();
type=t.charAt(0);
id=input.next();
if (type == 's') {
rate=input.nextDouble();
account = new SavingsAccount(date, id, rate);
} else {
credit=input.nextDouble();
rate=input.nextDouble();
fee=input.nextDouble();
account = new CreditAccount(date, id, credit, rate, fee);
}
// accounts.resize(accounts.getSize() + 1);
// accounts[accounts.getSize() - 1] = account;
accounts.add(account);
break;
case 'd': //存入现金
index=input.nextInt();
amount=input.nextDouble();
desc=input.next();
accounts.get(index).deposit(date, amount, desc);
break;
case 'w': //取出现金
index=input.nextInt();
amount=input.nextDouble();
desc=input.next();
accounts.get(index).withdraw(date, amount, desc);
break;
case 's': //查询各账户信息
for (int i = 0; i < accounts.size(); i++) {
System.out.print("["+i+"] ");
accounts.get(i).show();
System.out.println();
}
break;
case 'c': //改变日期
day=input.nextInt();
if (day < date.getDay())
System.out.println("You cannot specify a previous day");
else if (day > date.getMaxDay())
System.out.println("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 < accounts.size(); i++)
accounts.get(i).settle(date);
break;
}
} while (cmd != 'e');
for (int i = 0; i < accounts.size(); i++)
accounts.remove(i);
}
}
Accumulator.java
package java9_16;
//将某个数值按日累加
public class Accumulator {
private Date lastDate; //上次变更数值的时期
private double value,sum; //数值的当前值 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){
this.lastDate=date;
this.value=value;
this.sum=0;
}
//获得到日期date的累加结果
public final double getSum(final Date date) {
return sum + value * (date.operator(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;
}
}
Date.java
package java9_16;
//日期类
public class Date{
public final int[] DAYS_BEFORE_MONTH = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365 };
private int year,month,day,totalDays; //年 月 日 该日期是从公元元年1月1日开始的第几天
//用年、月、日构造日期
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("\n");
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 final int getYear() { return year; }
public final int getMonth() { return month; }
public final int getDay() { return day; }
//获得当月有多少天
public final int getMaxDay(){
if (isLeapYear() && month == 2)
return 29;
else
return DAYS_BEFORE_MONTH[month]- DAYS_BEFORE_MONTH[month - 1];
}
//判断当年是否为闰年
public final boolean isLeapYear() {
return year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
}
//输出当前日期
public final void show(){
System.out.println( getYear() + "-" + getMonth() + "-" + getDay() );
}
//计算两个日期之间差多少天
public final int operator (final Date date) {
return totalDays - date.totalDays;
}
}
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