为什么try-catch不能捕获IOException？

Question

在下面的代码中我得到了

Unreachable catch block for IOException

。这个异常永远不会从

try

语句的主体中抛出，错误（下划线）与

IOException

中的

} catch (IOException e){

。

我做错了什么？

class driver {

  public static void main(String[] args) {
    // TODO Auto-generated method stub
    Customer forrest = new Customer("Forrest Gump", 1,
        "42 New Street, New York, New York");
    Customer random = new Customer("Random Name", 2,
        "44 New Street, New York, New York");
    Customer customer[] = { null, forrest, random };
    int whichOption = 1;
    int id = 0;
    char action = ' ';
    char accSrc = ' ';
    char accDest = ' ';
    double amount = 0;
    BankAccount src = null;
    do {

      try{
        // process JOptionPane input information
        String input = JOptionPane
            .showInputDialog("Please enter your transaction information: ");
        Scanner s = new Scanner(input);
        id = Integer.parseInt(s.next());
        action = Character.toUpperCase((s.next().charAt(0)));

        if (action == 'T') {
          amount = s.nextDouble();
          accSrc = s.next().charAt(0);
          accDest = s.next().charAt(0);
        } else if (action == 'G' || action == 'I') {
          accSrc = s.next().charAt(0);
        } else {
          // if D,W
          amount = s.nextDouble();
          accSrc = s.next().charAt(0);
        }

      } catch (IOException e){

      }
      // taking action accordingly (T)ransfer, (D)eposit, (W)ithdraw, (I)nterest
      if (action == 'T') {

        (customer[id].getAccount(accSrc)).transfer(amount,
            customer[id].getAccount(accDest));
      } else if (action == 'G') {
        System.out.println("The current balance on your " + accSrc
            + " account is "
            + customer[id].getAccount(accSrc).getBalance() + "\n");
      } else if (action == 'D') {
        (customer[id].getAccount(accSrc)).deposit(amount);
      } else if (action == 'W') {
        (customer[id].getAccount(accSrc)).withdraw(amount);
      } else if (action == 'I') {
        (customer[id].getAccount(accSrc)).computeInterest();
      }
      whichOption = JOptionPane
          .showConfirmDialog(null , "Do you want to continue?");

      System.out.println("The balance on " + customer[id].getName()
          + " auto account is " + customer[id].A.balance);
      System.out.println("The balance on " + customer[id].getName()
          + " savings account is " + customer[id].S.balance);
      System.out.println("The balance on " + customer[id].getName()
          + " checkings account is " + customer[id].C.balance);
      System.out.println("The balance on " + customer[id].getName()
          + " loan account is " + customer[id].L.balance + "\n");

    } while (whichOption == 0);

  }
}

Answer 1

这是因为您在

try/catch

中执行的任何操作都不会抛出 IOException。

根据扫描仪javadoc

大多数 Scanner 类方法都会抛出

FileNotFoundException

（这不适用于您的情况，因为不从文件中读取）（或）

IllegalArgumentException

（或）

IllegalStateException

您需要将

IOException

更改为上述任一异常（或）删除 try/catch。

Answer 2

您可以删除 IOException 和 try catch，因为 try catch 中的任何语句都不会抛出此异常

Answer 3

似乎您在

try

块中所做的任何事情都没有抛出

IOException

Answer 4

该 try 块中的方法调用不会抛出

IOException

，这就是为什么 catch 是无法访问的代码。

您可以安全地删除 try 和 catch，因为这种情况永远不会发生。

Answer 5

您的

catch

块是空的，表明您无论如何都不会真正处理异常。您可能有一些代码让您捕获它，但现在您不再拥有它了。只要把周围的整个

try-catch

去掉就不会再有问题了

Answer 6

try/catch

块为空，代码不会抛出

IOException

，但可能会抛出其他异常。