JavaSE 05:面向对象-银行存款问题

设计一个账户类，其私有属性有账户余额，可实现取款和存款改变账户余额。再通过派生定义一个信用卡账户类，并在派生类中增加私有属性年利率，并增加方法计算月利息。
月利息=透支额×年利率/12
当账户余额大于或等于0时，透支额为0；当账户余额小于0时，透支额为账户余额的绝对值。
编写一个测试程序，先向信用卡账户中存款，再从信用卡账户中取款，最后根据透支额计算月利息，要求:
1、存款数、取款数和年利率从键盘上输入；
2、当账户余额大于或等于0时，输出账户余额；当账户余额小于0时，输出透支额和月利息。
Account:

package Day1;

public class Account {
      double surplus;
        public double getSurplus() {
            return this.surplus;
        }
        public void setSurplus(double  surplus) {
            this.surplus=surplus;
        }
        public Account() {
            this.surplus=0;
        }
        public Account(double  surplus) {
            this.surplus=surplus;
        }
        public double  deposit(double money) throws Exception{
            if(money<=0)
                throw new Exception("输入不正确！");
            return surplus+=money;
        }
        public double  widthdrawal(double money) throws Exception{
            if(money<=0||money>surplus)
                throw new Exception("输入不正确！");
            return surplus-=money;
        }

    }

creditcard :

package Day1;

public class creditcard extends  Account{
    private double rate;
    public double getRate() {
        return this.rate;
    }
    public void setRate(double rate) {
        this.rate=rate;
    }
    public creditcard() {

    }
    public creditcard(double surplus,double rate) {
        super(surplus);
        this.rate=rate;
    }
    public double interest() {
        if(surplus<0)
            return Math.abs(surplus)*rate/12;
        else
            return 0;
    }
}

Test:

package Day1;
import java.util.*;
public class Test {
    public static void main(String[] args) {
        try{
          Scanner sc=new Scanner(System.in);
            System.out.println("请输入存款金额：");
            double deposit=sc.nextDouble();
            System.out.println("请输入取款金额：");
            double widthdrawal=sc.nextDouble();
            System.out.println("请输入年利率：");
            double rate=sc.nextDouble();
            creditcard card=new creditcard ();
            card.setRate(rate);
            card.deposit(deposit);
            card.widthdrawal(widthdrawal);
            if(card.getSurplus()>=0)
                System.out.println("账户余额："+card.getSurplus());
            else
                System.out.println("透支额:"+ Math.abs(card.getSurplus())+" "+" "+"月利息："+ card.interest());

        }catch(Exception e) {
            e.printStackTrace();
        }

    }
}