java - 如何使用异常类，在主程序中捕获并处理异常

Question

我有一个程序，它接受用户关于游戏对象的信息，然后将游戏对象数组写入文件。我还需要使用我创建的异常类。如果用户输入的文档代码不是Sp、St或Gh，则需要抛出异常并捕获并处理，以允许用户尝试输入正确的代码。我认为我的异常类是正确的，但我真的不知道如何实现它。

public class InvalidDocumentCodeException extends Exception //Here is my exception class
{     
    public InvalidDocumentCodeException (String message)   
    { 
      super (message);       
    } 
}

import  java.util.Scanner;
import java.io.*;
public class  GamesList  
{   
  public static void  main (String[] args) throws InvalidDocumentCodeException, IOException     
  {      
    Scanner scan = new Scanner (System.in); 
    int count = 0, year;
    String doMore = "y"; 
    String file = "GameInfo.dat";
    String documentCode, title, developer;
    double price;

    FileWriter fw = new FileWriter (file);     
    BufferedWriter bw = new BufferedWriter (fw);     
    PrintWriter outFile = new PrintWriter (bw);

    //don't know if I need this
    InvalidDocumentCodeException problem = new InvalidDocumentCodeException ("Incorrect document code!!!");

    GameCollection games = new GameCollection();

    while (doMore.equalsIgnoreCase("y")) //lets user input data until they are done
    {
      System.out.println("Enter a valid document code (Sp, St, Gh):");
      documentCode = scan.nextLine();

      try     //my try catch
      {
        documentCode = "Sp";
      }
      catch(InvalidDocumentCodeException)
      {
        System.out.println("Oops! Try a valid code:");
        documentCode = scan.nextLine();
      }

      System.out.println("Enter the game name:");
      title = scan.nextLine();
      System.out.println("Enter the game developer:");
      developer = scan.nextLine();
      System.out.println("Enter the games release year:");
      year = scan.nextInt();
      System.out.println("Enter the games price:");
      price =  scan.nextDouble();

      games.addGame(documentCode, title, developer, year, price);

      System.out.println();
      System.out.println("This is great. Let's enter some more data. (Y/N):");

      doMore = scan.next();
      scan.nextLine();

      }
    outFile.println(games);
    System.out.println("Data written to GameInfo.dat");

    System.out.println(games);
    outFile.close();
  }
}

我环顾四周，但也许我只是不明白异常和 try catch 语句如何工作得足够好。

Answer 1

通常，您可以在需要的时间和地点创建并抛出异常。因此，例如，您可以这样:

try {
  // Do something
  if (somethingIsWrong) {
    throw new MyException("This is broke, yo!");
  }
} catch(MyException me) {
  // Write code to handle the exception or log it...
}

另一种方法是调用抛出异常的方法:

try {
  callToMethodThatThrowsSomeException(someVal);
} catch(SomeException se) {
  // Handle the exception here...
}

其中 callToMethodThatThrowsSomeException(someVal) 看起来像:

public void callToMethodThatThrowsSomeException(String someVal) throws SomeException {
  // Your code here, throwing a new SomeException for some reason...
}

在这种情况下，SomeException 将扩展 Exception。您可以让它扩展RuntimeException，在这种情况下，您不需要在方法签名上声明抛出。