以下实例是一个银行账户的模拟,通过银行卡的号码完成识别,可以进行存钱和取钱的操作。
InsufficientFundsException.java
文件代码:
// 文件名InsufficientFundsException.java
import java.io.*;
//自定义异常类,继承Exception类
public class InsufficientFundsException extends Exception
{
//此处的amount用来储存当出现异常(取出钱多于余额时)所缺乏的钱
private double amount;
public InsufficientFundsException(double amount)
{
this.amount = amount;//获取参数
}
public double getAmount()
{
return amount;
}
}
为了展示如何使用我们自定义的异常类,
在下面的 CheckingAccount
类中包含一个 withdraw()
方法抛出一个 InsufficientFundsException
异常。
CheckingAccount.java
文件代码:
// 文件名称 CheckingAccount.java
import java.io.*;
//此类模拟银行账户
public class CheckingAccount
{
//balance为余额,number为卡号
private double balance;
private int number;
public CheckingAccount(int number)
{
this.number = number;
}
//方法:存钱
public void deposit(double amount)
{
balance += amount;
}
//方法:取钱
public void withdraw(double amount) throws
InsufficientFundsException
{
if(amount <= balance)
{
balance -= amount;
}
else
{
double needs = amount - balance;
throw new InsufficientFundsException(needs);
}
}
//方法:返回余额
public double getBalance()
{
return balance;
}
//方法:返回卡号
public int getNumber()
{
return number;
}
}
下面的 BankDemo
程序示范了如何调用 CheckingAccount
类的 deposit()
和 withdraw()
方法。
BankDemo.java
文件代码:
//文件名称 BankDemo.java
public class BankDemo
{
public static void main(String [] args)
{
CheckingAccount c = new CheckingAccount(101);
System.out.println("Depositing $500...");
c.deposit(500.00);
try
{
System.out.println("\nWithdrawing $100...");
c.withdraw(100.00);
System.out.println("\nWithdrawing $600...");
c.withdraw(600.00);
}catch(InsufficientFundsException e)
{
System.out.println("Sorry, but you are short $"
+ e.getAmount());
e.printStackTrace();
}
}
}
编译上面三个文件,并运行程序 BankDemo
,得到结果如下所示:
Depositing $500...
Withdrawing $100...
Withdrawing $600...
Sorry, but you are short $200.0
InsufficientFundsException
at CheckingAccount.withdraw(CheckingAccount.java:25)
at BankDemo.main(BankDemo.java:13)