1

我正在尝试编写一个简单的程序，该程序从文本文件中读取整数，然后将总和输出到输出文件。我得到的唯一错误是在第 38 行“未解决的编译问题：文件无法解析”的 catch 块中。请注意，“文件”是我的输入文件对象的名称。如果我注释掉这个异常块，程序运行良好。任何意见，将不胜感激！

import java.io.*;
import java.util.Scanner;

public class ReadWriteTextFileExample 
{
    public static void main(String[] args) 
    {
        int num, sum = 0;

        try
        {
            //Create a File object from input1.txt
            File file = new File("input1.txt");
            Scanner input = new Scanner(file);

            while(input.hasNext())
            {
            //read one integer from input1.txt
                num = input.nextInt();
                sum += num;
            }
            input.close();  

        //create a text file object which you will write the output to
        File output1 = new File("output1.txt");
        //check whether the file's name already exists in the current directory
        if(output1.exists())
        {
            System.out.println("File already exists");
            System.exit(0);
        }
        PrintWriter pw = new PrintWriter(output1);
        pw.println("The sum is " + sum);
        pw.close();
    }
    catch(FileNotFoundException exception)
    {
        System.out.println("The file " + file.getPath() + " was not found.");
    }
    catch(IOException exception)
    {
        System.out.println(exception);
    }
}//end main method
}//end ReadWriteTextFileExample
4

2 回答 2

4

该file变量在try块内声明。它超出了catch块的范围。（尽管在这种情况下不可能发生，想象一下如果在执行甚至到达变量声明之前抛出异常。基本上，您无法访问catch在相应try块中声明的块中的变量。）

您应该在 try 块之前声明它：

File file = new File("input1.txt");
try
{
    ...
}
catch(FileNotFoundException exception)
{
    System.out.println("The file " + file.getPath() + " was not found.");
}
catch(IOException exception)
{
    System.out.println(exception);
}
于 2013-03-02T21:44:12.480 回答
3

Java 中的作用域是基于块的。您在块内声明的任何变量都只在同一块结束之前的范围内。

try 
{ // start try block
    File file = ...;

} // end try block
catch (...) 
{ // start catch block

  // file is out of scope!

} // end catch block

但是，如果您在块file之前声明try，它将保留在范围内：

File file = ...;

try 
{ // start try block


} // end try block
catch (...) 
{ // start catch block

  // file is in scope!

} // end catch block
于 2013-03-02T21:45:04.613 回答