实体类-银行账户余额推算表（Savings Account Class）

声明：金额计算未采用BigDecimal类。

代码如下：

package example;
//JHTP Exercise 8.5: Savings Account Class
//by pandenghuang@163.com
/**(Savings Account Class) Create class SavingsAccount. Use a static
* variable annualInterestRate to store the annual interest rate for
* all account holders. Each object of the class contains a private
* instance variable savingsBalance indicating the amount the saver
* currently has on deposit.Provide method calculateMonthlyInterest
* to calculate the monthly interest by multiplying the savingsBalance
* by annualInterestRate divided by 12—this interest should be added
* to savings-Balance. Provide a static method modifyInterestRate
* that sets the annualInterestRate to a new value. Write a program
* to test class SavingsAccount. Instantiate two savingsAccount objects,
* saver1 and saver2, with balances of $2000.00 and $3000.00, respectively.
* Set annualInterestRate to 4%, then calculate the monthly interest for
* each of 12 months and print the new balances for both savers. Next,
* set the annualInterestRate to 5%, calculate the next month’s interest
*  and print the new balances for both savers.
*/

class SavingAccount
{
public static double annualInterestRate;
private double savingsBalance;

public SavingAccount(double savingsBalance)
{
this.savingsBalance=savingsBalance;
}

public double calculateMonthlyInterest(){
savingsBalance+=savingsBalance*annualInterestRate/12;
return savingsBalance;
}

public static void modifyInterestRate(double annualIR){
annualInterestRate=annualIR;
}

}

public class SavingAccountTest
{
public static void main(String[] args)
{
SavingAccount saver1 = new SavingAccount(2000.00);
SavingAccount saver2 = new SavingAccount(3000.00);

SavingAccount.modifyInterestRate(0.04);
System.out.printf("本年度年利率为百分之%.2f，每月账户余额推算如下：\n",
100*SavingAccount.annualInterestRate);
System.out.println("月份\t储户1\t\t储户2");
for(int i=1;i<=12;i++){
System.out.printf("%d\t%.2f\t\t%.2f\n",i,saver1.calculateMonthlyInterest(),
saver2.calculateMonthlyInterest());
}

SavingAccount.modifyInterestRate(0.05);
System.out.printf("\n下一年度年利率为为百分之%.2f，每月账户余额推算如下：\n",
100*SavingAccount.annualInterestRate);
System.out.println("月份\t储户1\t\t储户2");
for(int i=1;i<=12;i++){
System.out.printf("%d\t%.2f\t\t%.2f\n",i,saver1.calculateMonthlyInterest(),
saver2.calculateMonthlyInterest());
}

}
}

运行结果：

本年度年利率为百分之4.00，每月账户余额推算如下：

月份 储户1 储户2

1 2006.67 3010.00

2 2013.36 3020.03

3 2020.07 3030.10

4 2026.80 3040.20

5 2033.56 3050.33

6 2040.33 3060.50

7 2047.14 3070.70

8 2053.96 3080.94

9 2060.81 3091.21

10 2067.68 3101.51

11 2074.57 3111.85

12 2081.48 3122.22

下一年度年利率为为百分之5.00，每月账户余额推算如下：

月份 储户1 储户2

1 2090.16 3135.23

2 2098.86 3148.30

3 2107.61 3161.42

4 2116.39 3174.59

5 2125.21 3187.82

6 2134.07 3201.10

7 2142.96 3214.44

8 2151.89 3227.83

9 2160.85 3241.28

10 2169.86 3254.78

11 2178.90 3268.35

12 2187.98 3281.96

测试数据：

与Excel中的计算结果一致。

2016	2016
Month	Account1	Account2	Month	Account1	Account2
Display	Display	Display	Display
1	2006.67	3010	1	2090.16	3135.23
2	2013.36	3020.03	2	2098.86	3148.3
3	2020.07	3030.1	3	2107.61	3161.42
4	2026.8	3040.2	4	2116.39	3174.59
5	2033.56	3050.33	5	2125.21	3187.82
6	2040.33	3060.5	6	2134.07	3201.1
7	2047.14	3070.7	7	2142.96	3214.44
8	2053.96	3080.94	8	2151.89	3227.83
9	2060.81	3091.21	9	2160.85	3241.28
10	2067.68	3101.51	10	2169.86	3254.78
11	2074.57	3111.85	11	2178.9	3268.35
12	2081.48	3122.22	12	2187.98	3281.96