Not able to use Multi Catch from Java Effectively [duplicate]

问题

This question already has answers here:

What is a NumberFormatException and how can I fix it? [duplicate] (9 answers)

Why does order matter when catching exceptions? (8 answers)

Closed 3 years ago.

I really want to use features from Java-1.7. One of this feature is "Multi-Catch". Currently I have the following code

try {
    int Id = Integer.parseInt(idstr);

    TypeInfo tempTypeInfo = getTypeInfo(String.valueOf(Id));

    updateTotalCount(tempTypeInfo);
} catch (NumberFormatException numExcp) {
    numExcp.printStackTrace();
} catch (Exception exception) {
    exception.printStackTrace();
}

I want to remove the two catch blocks from the above code, and instead use single catch like below:

try {
    int Id = Integer.parseInt(idstr);

    TypeInfo tempTypeInfo = getTypeInfo(String.valueOf(Id));

    updateTotalCount(tempTypeInfo);
} catch (Exception | NumberFormatException ex) { // --> compile time error
    ex.printStackTrace();
}

But the above code is giving compile time error:

"NumberFormatException" is already caught by the alternative Exception.

I understood the above compile time error but what is the replace for my first block of code.

回答1:

NumberFormatException is a subclass of Exception. Saying that both catch blocks should have the same behavior is like saying that you don't have any special treatment for NumberFormatException, just the same general treatment you have for Exception. In that case, you can just omit its catch block and only catch Exception:

try {
    int Id = Integer.parseInt(idstr);

    TypeInfo tempTypeInfo = getTypeInfo(String.valueOf(Id));

    updateTotalCount(tempTypeInfo);
} catch (Exception exception) {
    exception.printStackTrace();
}

回答2:

The compiler is telling you that

} catch (Exception ex) {

will also catch NumberFormatException exceptions because java.lang.NumberFormatException extends java.lang.IllegalArgumentException, which extends java.lang.RuntimeException, which ultimately extends java.lang.Exception.

回答3:

The types in multi-catch must be disjoint and java.lang.NumberFormatException is a subclass of java.lang.Exception.

回答4:

In this case multi-catch is not required because NumberFormatException is derived from Exception. You can simply catch only Exception to get them both. If you need another handling for NumberFormatException than for other exceptions, you must use the example you posted first.

回答5:

you can use

    try {
    int Id = Integer.parseInt(idstr);

    TypeInfo tempTypeInfo = getTypeInfo(String.valueOf(Id));

    updateTotalCount(tempTypeInfo);
  } catch (Exception exception) {
    exception.printStackTrace();
  }

回答6:

To add on to Mureinik's solution:

If you would like to differentiate the error handling for each of the subclasses you could use instanceof within the catch block something like:

FileNotFoundException is subclass of IOException

catch (IOException e) {
            if (e instanceof FileNotFoundException)
            {
                System.out.println("FileNotFoundException");
            }
            else if(e instanceof IOException)
            {
                System.out.println("IOException");
            }

        }

回答7:

Exception is the parent class of all exceptions and ideally (Preferred approach - Best Coding Practice), you should never catch Exception unless you are not sure what is going to be thrown at Runtime in try block.

Since, in your code you are doing NumberFormat operation, which is a child class of Exception, you should not catch Exception (unless other 2 methods may throw unchecked exception) and instead, use:

try {
    int Id = Integer.parseInt(idstr);
    TypeInfo tempTypeInfo = getTypeInfo(String.valueOf(Id));\
    updateTotalCount(tempTypeInfo);
} catch (NumberFormatException npe) {
    npe.printStackTrace();
}

来源：https://stackoverflow.com/questions/32345287/not-able-to-use-multi-catch-from-java-effectively

标签

java

exception

try-catch

numberformatexception

multi-catch