CS61b lab6

主要加深了对Exception用法的理解，以前一直不太清楚。

part1：在main中多加了一个try和catch块。

part2 part3：

将VirtualTeller和AccountData中的方法抛出异常并在BankApp中处理。

最开始抛出两行异常，更改后只抛出一行。另外，part1中说的withdraw的小bug应该是输入负数时没有抛出错误信息吧。

更改过的方法：

public class BadTransactionException extends Exception {
BadTransactionException(int i){
    super("Invalid amount number "+i);
}
}

public void withdraw(int amt) throws BadTransactionException {
    if (amt <= balance&&amt>=0) {
      balance = balance - amt;
    } else {
      throw new BadTransactionException(amt);
    }
  }

  /**
   *  deposit() deposits "amt" dollars into this account.
 * @throws BadTransactionException 
   **/
  public void deposit(int amt) throws BadTransactionException {
    if (amt >= 0) {
      balance = balance + amt;
    } else {
      throw new BadTransactionException(amt);
    }
  }

public void withdraw(int acct, int amount) throws BadAccountException, BadTransactionException {
   AccountData account = findAccount(acct);
   account.withdraw(amount);
  
  }

  /**
   *  deposit() deposits "amount" dollars into the bank account whose number is
   *  "acct".  Assumes that amount >= 0.  If "acct" is invalid, no action is
   *  taken.
   *  @param acct is an account number.
   *  @param amount an amount of money.
 * @throws BadAccountException 
 * @throws BadTransactionException 
   */
  public void deposit(int acct, int amount) throws BadAccountException, BadTransactionException {
    AccountData account = findAccount(acct);
      account.deposit(amount);
   }

  /**
   *  balanceInquiry() finds the balance on the account whose number is "acct".
   *  If "acct" is an invalid number, returns -1.
   *  @param acct an account number.
   *  @return the balance, or -1 if the account number is invalid.
 * @throws BadAccountException 
   */
  public int balanceInquiry(int acct) throws BadAccountException {
  
       AccountData account = findAccount(acct);
       return account.getBalance();
  }
  

  /**
   *  findAccount() gets the AccountData object associated with account number
   *  "acct".  If "acct" does not refer to a valid account, returns null.
   *  @param acct is an account number.
   *  @return the AccountData object associated with the account number.
 * @throws BadAccountException 
   */
  private AccountData findAccount(int acct) throws BadAccountException  {
      
    AccountData account = (AccountData) accounts.find(acct);
    if(account==null)
            throw new BadAccountException(acct);
    return account;
 
  }

private void doDeposit() throws IOException {
    // Get account number.
    int acctNumber = readInt("Enter account number: ");
    int amount = readInt("Enter amount to deposit: ");
try
    {ATM.deposit(acctNumber, amount);
    System.out.println("New balance for #" + acctNumber + " is " +
                       ATM.balanceInquiry(acctNumber));}
catch(Exception e){
    System.out.println(e);
    doDeposit();
}
    
  }

  /**
   *  doWithdraw() prompts the user for an account number and tries
   *  to perform a withdrawal transaction from that account.
   *  @exception IOException if there are problems reading user input.
   */
  private void doWithdraw() throws IOException {
    // Get account number.
    int acctNumber = readInt("Enter account number: ");
    int amount = readInt("Enter amount to withdraw: ");
try{
    ATM.withdraw(acctNumber, amount);
    System.out.println("New balance for #" + acctNumber + " is " +
                       ATM.balanceInquiry(acctNumber));
}catch(Exception e){
    System.out.println(e);
    doWithdraw();
}
  }

  /**
   *  doInquire() prompts the user for an account number, then attempts to
   *  discover and print that account's balance.
   *  @exception IOException if there are problems reading user input.
   */
  private void doInquire() throws IOException {
    int acctNumber = readInt("Enter account number: ");

   try{ System.out.println("Balance for #" + acctNumber + " is " +
                       ATM.balanceInquiry(acctNumber));}
   catch(Exception e){
       System.out.println(e);
       doInquire();
   }
  }

最后的附加题：提示说只需要多加一行，应该就是在catch块的最后再加一个recursion就好了。