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Checked Exceptions

 
Greenhorn
Posts: 6
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Hi,
I have a question about checked exceptions. I have seen the folowing statement:
"When you extend a class & override a
method, the new method can not be declared as throwing checked
Exceptions other than those that were declared by the original
method."
Ex: (from RHE)
public Base {
public int Amethod () throws IOException {}
}
public Sub1 extends Base {
public int Amethod () throws IOException {} // ok
}
public Sub2 extends Base {
public int Amethod () throws IOException {} // ok
}
public Sub3 extends Base {
public int Amethod () {} // illegal
}
public Sub4 extends Base {
public int Amethod () throws Exception {} // illegal
}
public Sub5 extends Base {
public int Amethod () throws MalformedException {} // ok
}
I do not understand why Sub3 Amethod & Sub4 Amethod are illegal
& the Sub5 Amethod is ok.
Fernando
 
Ranch Hand
Posts: 38
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hi fernando ,
i think sub3 should be legal .
sub4 is correct and sub5 is also legal .
bcoz as per rule overriding method can throw exceptions , those r thrown by overridden method or can throw exceptions those r subclass of the exception thrown by overridden method .this is true only for checked exceptions .
so as per rule sub4 is throwing an exception which is base class exception of amethod()which is illegal and sub5 is throwing an exception which is subclass of ioexception so legal .
only doubt is about sub3
actually sub3 should work .
so please check that out again .
bye rahul
 
Ranch Hand
Posts: 67
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hi Fernando
i think that if u declare in a super class that a method throws an exception, then u over ride that method in a subclass without declaring that it throws an exception, that is illegal.
 
lee dalais
Ranch Hand
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but then again i tried similiar code and it didn't give any problem.
 
Greenhorn
Posts: 24
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Hi,
When you override a method, the overriding method cannot throw any checked exception not thrown by the overriden one.
So if a method m() in class Super throws a IOException and we override m() in class Sub that extends Super, then if m() in Sub declares that throws any checked exception, they have to be IOException or a subclass of it.
So the method in Sub3 is ok

 
Ranch Hand
Posts: 103
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Lee I think when you override a method that throws checked exceptions you must either declare the same exception or a subclass exception of the one declared in the overridden method or you don't have to declare any exceptions in the overriding method.
 
Consider Paul's rocket mass heater.
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