java - 创建用户定义的异常类-获取 null 作为答案(JAVA)

Question

我尝试实现以下问题，但在尝试将值传递给方法时得到 null 作为答案。提现时计算新余额后，我似乎无法将值传递给方法transfer。

帐户类别:

package Number3;

public class Account {

private int balance;
private int maxTransfer;

public Account()
{
    balance = 0;
    maxTransfer = 0;
}

public Account(int bal,int maxT)
{
    balance = bal;
    maxTransfer = maxT;
}

public void setBalance(int b)
{
    balance = b;
}

public int getBalance()
{
    return balance;
}

public void setMaxTransfer(int m)
{
    this.maxTransfer = m;
}

public int getMaxTransfer()
{
    return maxTransfer;
}

public void withdraw(int amount) throws insufficientFundException
{
    if(!(amount < balance))
    {
        balance = balance - amount;
    }
    else
    {
        throw new insufficientFundException();
    }
}

public void transfer(int amount)
{
    balance = amount + balance;
}

public void display()
{
    System.out.println("Current balance: "+getBalance());
}
}

testAccount 主要:

package Number3;
import java.util.Scanner;

public class testAccount{

public static void main(String[] args) {

    try{
    Account a = new Account();
    a.setBalance(1000);
    a.setMaxTransfer(10000);
    int choice,amount,acc;

    Scanner input = new Scanner(System.in);

    a.display();

    System.out.println("1. Withdraw \t\t 2. Transfer");
    System.out.println("Choose either 1 or 2");
    choice = input.nextInt();

    switch(choice)
    {
    case 1:
    {
        System.out.println("Enter amount to withdraw: ");
        amount = input.nextInt();
        a.withdraw(amount); //where i assume the error is
        a.getBalance();
        break;
    }
    case 2:
    {
        System.out.println("Enter amount to transfer: ");
        amount = input.nextInt();
        a.transfer(amount);
        a.getBalance();
        break;
    }
    default:
    {
        System.out.print("Enter 1 or 2: ");
        choice = input.nextInt();
    }
    }


}
catch(insufficientFundException ife)
{
    System.out.print(ife.getMessage());
}

}
}

以及用户定义的异常的类:

package Number3;

public class insufficientFundException extends Exception{

public static void main(String[] args) {
    System.out.println("You don't have enough funds in your account.");

}

}

请告诉我我做错了什么。谢谢。

Answer 1

这个 main 方法永远不会被调用。将异常添加到构造函数中的父类(super class)

package Number3;

public class insufficientFundException extends Exception{

    insufficientFundException(String msg){
       super(msg);
    }

}

在您的代码中发生此异常时抛出

if(balance-withdrawal<0){
   throw new insufficientFundException("Your error message");
}