A question about exceptions

[Jix]

Sorry for the long post But I'm really confused with Exceptions, I noticed that sometimes when an exception occurs in a method, the method has to declare that it throws this exception. And sometimes it's not necessary to declare that it throws this Exception. I noticed that it depends on the exception itself. example:

class A {
public void doA() { throw new Exception("Exception"); }

public static void main(String[] args) {
A a = new A();
try{
a.doA();}
catch(Exception e){ }
}
}


This code fails to compile because there is unreported Exception. But if I changed the Exception to NullPointerException then it will compile as in:

class A {
public void doA() { throw new NullPointerException("Exception");}

public static void main(String[] args) {
A a = new A();
try{
a.doA();}
catch(Exception e){ }
}
}


So what kind of exceptions that require method to declare that it throws exceptions?

Thanks for your time

[admin]

The rule is very simple. Any exception class that extends from RuntimeException or Error need not be declared in the throws clause. These exceptions are called unchecked exceptions because you don't have to check/acknowledge the possibility of them being thrown. NullPointerException is such an exception.

All other exceptions have to be either caught in a try/catch block or have to be declared in the throws clause. These are therefore called checked exceptions. java.lang.Exception is a checked exception.

There is a small write up on common exception classes in the Study Refs section of the simulator. You might want to take a look at that as they are important for the exam.

HTH,
Paul.

[Adlearee]

The answer is correct but i will try to put it even more simply than this. There are two classes of exceptions - checked and unchecked. Checked exceptions are the ones which the compiler acutally checks for and these have to be either handled in try catch blocks, or declared to be thrown. Unchecked exceptions are no problems. The code will work even wiothout decalring them as thrown.

[Jix]

Ok thanks a lot, I tried now to check the reference but it told me that Access is denied.

[admin]

Ok thanks a lot, I tried now to check the reference but it told me that Access is denied.

It is trying to extract the document and unable to create it in the local file system. Try running the application as administrator.

[Jix]

It worked, thanks