在一个catch块中处理所有Java异常

Question

When I try to write this code :

catch (Exception  | OutOfMemoryError| NumberFormatException| SQLException| IOException  e){
}

I get the error: "The exception NumberFormatException is already caught by the alternative Exception" I understand it great and from first thinking it's make sense because Exception is the general one. but when I write this code:

 catch (Exception  | OutOfMemoryError  e){
    }

It works without any problems so now I start to get confused why don't I get the previous error. Is OutOfMemmoryError will catch things that Exception won't catch? If I Want to make catch that will include all of exceptions and errors possible what should i write? I just understood that this:

catch (Exception e){
}

won't catch for me all the exceptions and errors so what will do it?

Answer 1

The code catch (Exception | OutOfMemoryError e){ } compiles because OutOfMemoryError is not an Exception , so Exception doesn't cover OutOfMemoryError . OutOfMemoryError is an Error and it is not an Exception .

It's usually not a good idea to catch Error s, because they are usually unrecoverable anyway.

Answer 2

To better understand what's happening, take a look at the Java exception hierarchy. A broad overview can be seen in this diagram .

When you catch multiple exceptions in a single catch block, you should only use the "topmost" exceptions in catch. For example, your error will persist in something like

catch (IOException | FileNotFoundException e)

since FileNotFoundException extends IOException .

In your code, all exceptions (except OutOfMemoryError ) are subtypes of java.lang.Exception , hence the error. OutOfMemoryError is a subtype of java.lang.Error , which is a Throwable , but not an Error .

Here is a more fine-grained diagram representing the hierarchy of all java.lang.Exception s within Throwable .

Hope this helped.

Finally, if you really want to catch all exceptions and errors in one catch block (a terrible idea, as others have pointed out), you could do one of the following:

catch (Exception | Error e)

or

catch (Throwable t)

Answer 3

You can catch Throwable , which is a superclass of everything, that can be thrown, errors or exceptions.

As pointed out previously though, this is not a good idea, and not something you should do. You should only be catching those exceptions from which you can meaningfully recover.

Answer 4

不允许在multi-catch语句中指定相同层次结构的两个或多个异常。

Answer 5

如果您想捕获“所有内容”，则可以捕获（Throwable t）捕获错误，异常，运行时异常等。尽管我建议捕获单个异常，因为您可能希望应用程序处理不同类型的异常/错误。 /不同。