尝试/捕获未找到的文件异常嵌套在当时循环中

Question

我试图在while循环中为“未找到文件”异常编写代码，以便程序继续提示用户输入文件（test.txt）。我在while循环中编写了一个try/catch块。但是，当我删除输入文件（test.txt）时，程序应捕获此错误并打印“error，找不到'test.txt'文件，请重试：”并允许用户输入另一个文件名。然而，该程序崩溃，并给我一个FileNotFoundException。

Answer 1

在您的代码中，两行引发您未捕获的FileNotFoundException：

// scanner and printwriter objects for reading text file
Scanner in = new Scanner(correctInputfile);
PrintWriter out = new PrintWriter(outputName);
// read input (values) and write the output (average)

您可以用下面的代码替换它们，代码应该可以工作。

Scanner in = null;// Initialize to null, so they don't raise warnings.
PrintWriter out = null;
try { // Surround with try/catch to get the exception
    in = new Scanner(correctInputfile);
    out = new PrintWriter(outputName);
}catch(FileNotFoundException e){
    /*TODO: something about the exception here!
      Make sure the Scanner and PrintWriter get 
      properly initialized with valid file names.*/
}

Answer 2

您应该为扫描仪添加另一个尝试和捕获

// prompt user for name for output textfile
System.out.println();
System.out.print("What would you like to call your output file: ");
String outputName = inputReader.nextLine();
// scanner and printwriter objects for reading text file
try {
    Scanner in = new Scanner(correctInputfile);
    PrintWriter out = new PrintWriter(outputName);
    // read input (values) and write the output (average)

    // messages triggered by successful location of files.
    if (fileName.equalsIgnoreCase(("test_input.txt"))) {
        // code logic
    }
} catch (FileNotFoundException ex) {
    System.out.println();
    System.out.println("***** ERROR *****");
    System.out.println("\nCannot locate the input file " + "'" + fileName + "'" + "on your computer - please try again.");
    System.out.print("\nInput file name (from your computer): ");
}

Answer 3

在这种情况下，最好是请求许可而不是宽恕（例如，在尝试读取文件之前检查文件是否存在）。

File file = new File("test_input.txt");
if (file.exists()) {
    FileReader fileReader = new FileReader(file);
}