我可以避免Java中的catch块吗？ [英] Can I avoid catch block in Java?

问题描述

在一种方法中，我使用扫描仪读取文件中的文本。该文件并不总是存在，如果不存在，我只是想什么也不做（即不扫描）。
当然，我可以这样使用try / catch：

Inside a method, I use a Scanner to read text inside a file. This file doesn't always exist, and if it doesn't, I want simply to do nothing (i.e. no scan). Of course I could use a try/catch like this:

String data = null;
try
{
    Scanner scan = new Scanner(new File(folder + "file.txt"));
    data=scan.nextLine();
    scan.close();
}
catch (FileNotFoundException ex)
{
}

我的问题是我该怎么做才能避免尝试/捕获？因为我不喜欢未使用的局部变量。我在想类似的东西：

My question is what can I do to avoid the try/catch? Because I don't like local variable unused. I was thinking of something like:

String data = null;
File file_txt = new File(folder + "file.txt");
if (file_txt.exists())
{
    Scanner scan = new Scanner(file_txt);
    data=scan.nextLine();
    scan.close();
}

但是，与此同时，我在Netbeans中遇到了一个错误，但我无法建立我的项目...

But of course with this I get an error in Netbeans and I can't build my project...

推荐答案

否，已检查异常。 try 之后必须是 catch 块和/或最终块。有两种方法可以处理受检查的异常。

No, It's checked exception. try must be followed with either catch block and/or finally block. There are two method for handling checked exception.

方法1：可以使用 try / catch / finally

Method 1 : Either wrap your code using try/catch/finally

选项1

try{
    Scanner scan = new Scanner(new File(folder + "file.txt"));
    data=scan.nextLine();
    scan.close();

}
catch (FileNotFoundException ex)
{
   System.out.println("Caught " + ex);
}

选项2

try{
    Scanner scan = new Scanner(new File(folder + "file.txt"));
    data=scan.nextLine();
    scan.close();

}
finally
{ 
      System.out.println("Finally ");
}

选项3

    try{ 
     Scanner scan = new Scanner(new File(folder + "file.txt"));
     data=scan.nextLine();
     scan.close();
     }catch(FileNotFoundException ex){
          System.out.println("Caught " + ex );
     }finally{
          System.out.println("Finally ");
     }  

方法2：使用 throw抛出异常并列出所有带有 throws 子句的异常。

Method 2: Throw exception using throw and list all the exception with throws clause.

    class ThrowsDemo {

    static void throwOne() throws IllegalAccessException {
        System.out.println("Inside throwOne.");
        throw new IllegalAccessException("demo");
    }

    public static void main(String args[]) {
        try {
            throwOne();
        } catch (IllegalAccessException e) {
            System.out.println("Caught " + e);
        }
    }
    }

注意：已检查的异常表示编译器会强制您编写一些内容来处理此错误/异常。因此，AFAIK除了上述方法外，没有其他方法可以用于检查异常。

Note : Checked Exception means Compiler force you to write something to handle this error/exception. So, AFAIK, there is no any alternative for checked exception handling except above method.

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