2.建立exception包，建立Bank类，类中有变量double balance表示存款,Bank类的构造方法能增加存款，Bank类中有取款的发方法withDrawal(double dAmount),当取款的数额大于存款时,抛出InsufficientFundsException,取款数额为负数，抛出NagativeFundsException,

public class Bank {

    Double qian=0.0;

    double newBank(double a)

    {

        qian=qian+a;

        return qian;

    }

    double withDrawal(double dAmount) throws Exception

    {

        if(dAmount>qian)

        {

            throw new Exception("InsufficientFundsException");

        }

        if(dAmount<0)

        {

            throw new Exception("NagativeFundsException");

        }

        qian=qian-dAmount;

        return qian;

    }

   public static void main(String[] args) throws Exception {

       Bank a=new Bank();

       a.newBank(100);

       a.withDrawal(-50);

}

}

   public static void main(String[] args) throws Exception {

       Bank a=new Bank();

       a.newBank(100);

       a.withDrawal(150);

}