为什么选择Java Runtime - unChecked异常需要子类

Question

Java Runtime Exception is used to check un-checked exception. It is accepted standard that to sub class JavaRunTimeException. Can you please explain me the reason behind sub classing without directly using it as below.

try {
    int x = Integer.parseInt(args[0])/Integer.parseInt(args[0]);
} catch (RuntimeException e) {

}

Recommended approach

public class ServiceFaultException extends RuntimeException {}

try {
    int x = Integer.parseInt(args[0])/Integer.parseInt(args[0]);
} catch (ServiceFaultException e) {

}

I would like to know reasons for this recommendation. ?

Answer 1

Exceptions are used to give some meaning to an error that is not handled right away where it occurs. Subclassing RuntimeException allows you to give more meaning and differentiate between several RuntimeExceptions .

For instance, it is useful to be able to tell the difference between IllegalArgumentException and NumberFormatException , which are both RuntimeException s.

EDIT: As @Dyrborg said, catching RuntimeException can also be dangerous because anything could throw it without your knowledge. Better handle only what you control.

ASIDE: You could tell me "why not a checked Exception then ?". I usually use RuntimeException s when it corresponds to an incorrect use of a method (illegal argument for instance). It means something the programmer can ensure to avoid. When it comes to user input, or internet connection, which is not reliable, then Exception s are more appropriate, because the programmer must handle these error cases.

Answer 2

Can you please explain me the reason behind sub classing without directly using it as below.

The same reason as applies to subclassing any other exception. The language provides the facility to catch specific subclasses, so why wouldn't you use it?