我可以在Java中避免catch语句吗？ [英] Can I avoid catch statement in Java ?

问题描述

在一个方法中，我使用扫描器来读取文件中的文本。这个文件并不总是存在，如果没有，我只想做什么（也就是没有扫描）。
当然我可以使用这样的try / catch：

  String data = null; 
尝试
 {
扫描仪扫描=新扫描仪（新文件（文件夹+file.txt））; 
 data = scan.nextLine（）; 
 scan.close（）; 
} 
 catch（FileNotFoundException ex）
 {
} 
  

我的问题是我可以做些什么来避免try / catch？因为我不喜欢本地变量未使用。我在想这样的事情：

  String data = null; 
文件file_txt =新文件（文件夹+file.txt）; 
 if（file_txt.exists（））
 {
扫描仪扫描=新扫描仪（file_txt）; 
 data = scan.nextLine（）; 
 scan.close（）; 
} 
  

但是当然这样我在Netbeans中收到错误，我不能构建我的项目...

解决方案

否，它被检查异常。 尝试必须遵循 catch 块和/或 finally 阻止。有两种处理检查异常的方法。

方法1：使用包装你的代码try / catch / finally

选项1

 code> try {
扫描仪扫描=新扫描仪（新文件（文件夹+file.txt））; 
 data = scan.nextLine（）; 
 scan.close（）; 
 
} 
 catch（FileNotFoundException ex）
 {
 System.out.println（Caught+ ex）; 
} 
  

选项2

 尝试{
扫描仪扫描=新扫描仪（新文件夹（文件夹+file.txt））; 
 data = scan.nextLine（）; 
 scan.close（）; 
 
} 
 finally 
 {
 System.out.println（Finally）; 
} 
  

选项3

 尝试{
扫描仪扫描=新扫描仪（新文件夹（文件夹+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例外与 throws 子句。

  class ThrowsDemo {
 
 static void throwOne（）throws IllegalAccessException {
 System.out.println（Inside throwOne。）; 
抛出新的IllegalAccessException（demo）; 
} 
 
 public static void main（String args []）{
 try {
 throwOne（）; 
} catch（IllegalAccessException e）{
 System.out.println（Caught+ e）; 
} 
} 
} 
  

注意： / strong>检查异常意味着编译器强制你写一些东西来处理这个错误/异常。所以，AFAIK，除了上述方法之外，没有任何替代检查的异常处理。

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)
{
}

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();
}

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

解决方案

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.

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

Option 1

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

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

Option 2

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

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

Option 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 ");
     }  

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);
        }
    }
    }

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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