Java Try and Catch IOException 问题

Java Try and Catch IOException Problem

提问by ubiquibacon

I am trying to use a bit of code I found at the bottom of this page. Here is the code in a class that I created for it:

我正在尝试使用我在本页底部找到的一些代码。这是我为它创建的类中的代码：

import java.io.LineNumberReader;
import java.io.FileReader;
import java.io.IOException;

public class LineCounter {
  public static int countLines(String filename) throws IOException {
    LineNumberReader reader  = new LineNumberReader(new FileReader(filename));
    int cnt = 0;
    String lineRead = "";
    while ((lineRead = reader.readLine()) != null) {}
    cnt = reader.getLineNumber();
    reader.close();
    return cnt;
  }
}

My objective is to count the lines of a text file, store that number as an integer, then use that integer in my main class.In my main class I tried a few different ways of making this happen, but (being a new programmer) I am missing something. Here is the first thing I tried:

我的目标是计算文本文件的行数，将该数字存储为整数，然后在我的主类中使用该整数。在我的主要课程中，我尝试了几种不同的方法来实现这一点，但是（作为一名新程序员）我错过了一些东西。这是我尝试的第一件事：

String sFileName = "MyTextFile.txt";
private int lineCount = LineCounter.countLines(sFileName);

With this attempt I get the error "unreported exception java.io.IOException; must be caught or declared to be thrown." I don't understand why I am getting this because as I can see the exception is declared in my "countLines" method. I tried to use a try catch block right under that last bit of code I posted, but that didn't work either (I don't think I did it right though). Here is my try catch attempt:

通过这次尝试，我得到了错误“未报告的异常 java.io.IOException；必须被捕获或声明为被抛出”。我不明白为什么我会得到这个，因为我可以看到异常是在我的“countLines”方法中声明的。我试图在我发布的最后一段代码下使用 try catch 块，但这也不起作用（尽管我认为我做得不对）。这是我的 try catch 尝试：

String sFileName = "MyTextFile.txt";
private int lineCount;{
    try{
        LineCounter.countLines(sFileName);
    }
    catch(IOException ex){
        System.out.println (ex.toString());
        System.out.println("Could not find file " + sFileName);
    }
}

Please show me the way! Thanks in advance for your help!

请给我指路！在此先感谢您的帮助！

采纳答案by polygenelubricants

Initializer block is just like any bits of code; it's not "attached" to any field/method preceding it. To assign values to fields, you have to explicitly use the field as the lhs of an assignment statement.

初始化块就像任何代码位一样；它没有“附加”到它之前的任何字段/方法。要将值分配给字段，您必须明确使用该字段作为赋值语句的 lhs。

private int lineCount; {
    try{
        lineCount = LineCounter.countLines(sFileName);
        /*^^^^^^^*/
    }
    catch(IOException ex){
        System.out.println (ex.toString());
        System.out.println("Could not find file " + sFileName);
    }
}

Also, your countLinescan be made simpler:

此外，您countLines可以更简单：

  public static int countLines(String filename) throws IOException {
    LineNumberReader reader  = new LineNumberReader(new FileReader(filename));
    while (reader.readLine() != null) {}
    reader.close();
    return reader.getLineNumber();
  }

Based on my test, it looks like you can getLineNumber()after close().

根据我的测试，看起来你可以getLineNumber()在close().

回答by brabster

Your countLines(String filename)method throws IOException.

您的countLines(String filename)方法抛出 IOException。

You can't use it in a member declaration. You'll need to perform the operation in a main(String[] args)method.

您不能在成员声明中使用它。您需要在main(String[] args)方法中执行操作。

Your main(String[] args)method will get the IOException thrown to it by countLines and it will need to handle or declare it.

您的main(String[] args)方法将获得 countLines 向其抛出的 IOException，它需要处理或声明它。

Try this to just throw the IOException from main

试试这个只是从 main 抛出 IOException

public class MyClass {
  private int lineCount;
  public static void main(String[] args) throws IOException {
    lineCount = LineCounter.countLines(sFileName);
  }
}

or this to handle it and wrap it in an unchecked IllegalArgumentException:

或者这个来处理它并将它包装在一个未经检查的 IllegalArgumentException 中：

public class MyClass {
  private int lineCount;
  private String sFileName  = "myfile";
  public static void main(String[] args) throws IOException {
    try {
      lineCount = LineCounter.countLines(sFileName);
     } catch (IOException e) {
       throw new IllegalArgumentException("Unable to load " + sFileName, e);
     }
  }
}

回答by JasCav

The reason you are getting the the IOException is because you are not catching the IOException of your countLines method. You'll want to do something like this:

您获得 IOException 的原因是因为您没有捕获 countLines 方法的 IOException。你会想要做这样的事情：

public static void main(String[] args) {
  int lines = 0;  

  // TODO - Need to get the filename to populate sFileName.  Could
  // come from the command line arguments.

   try {
       lines = LineCounter.countLines(sFileName);
    }
    catch(IOException ex){
        System.out.println (ex.toString());
        System.out.println("Could not find file " + sFileName);
    }

   if(lines > 0) {
     // Do rest of program.
   }
}