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);

}