classes with constructors throwing exceptions

[kevinn lee]

"instantiating of classes having constructors that throw exceptions is not possible"
as far as I know this is correct because the procedure of creating the object wont complete because of the exception.Am I correct?

[Ankit Garg]

1. Where did you read that statement
2. If that statement is talking about constructors that have some exceptions in their throws clause, then the statement is wrong. You can create instances of such classes, you just have to wrap the instantiation in a try-catch block...

[kevinn lee]

Ankit Garg wrote:1. Where did you read that statement
2. If that statement is talking about constructors that have some exceptions in their throws clause, then the statement is wrong. You can create instances of such classes, you just have to wrap the instantiation in a try-catch block...

you mean like the following

   
class E1 extends Exception{}


class Q104{
Q104()throws E1{
	throw new E1();
}
public static void main(String[] args){
try{	Q104 q=new Q104();
}catch(E1 e){
}
System.out.print(q);//1
}} 

Since the compiler says that variable q is unknown(line 1) I thought the instantiation process has not completed.Am I wrong?
thanks

[Rajeev Rnair]

This is because you have declared q inside the try block. It is not accessible outside the try block. Please declare "q" outside "try" as in code below.
Small request . Please write more readable code if you can

class E1 extends Exception{}   

class Q104{   
	Q104()throws E1{   
		throw new E1();   
	}   
	public static void main(String[] args){   
		Q104 q = null;
		try{
			q=new Q104();   
		}catch(E1 e){   
		}   
		System.out.print(q);//1   
	}
}   

[kevinn lee]

Rajeev Rnair wrote:This is because you have declared q inside the try block. It is not accessible outside the try block. Please declare "q" outside "try" as in code below.
Small request . Please write more readable code if you can

sorry about the untidy code.
but even here I cant see object initialization taking place.Output is "null".How should the code change in order to make sure that a object is initialized?
thanks

[Prithvi Sehgal]

Hi,

How do you expect that object will be created and initialized when you are throwing
exception from within the constructor. It will never complete. Try omitting the line which
is again throwing the exception within the constructor.

Hope this helps,

[kevinn lee]

Prithvi Sehgal wrote:Hi,

How do you expect that object will be created and initialized when you are throwing
exception from within the constructor. It will never complete. Try omitting the line which
is again throwing the exception within the constructor.

Hope this helps,

hello

the statement is correct then?
thanks prithvi

[Prithvi Sehgal]

Kevin,

As Ankit has quoted it is applicable to the throws clause. For example

   

//case 1
public SomeConstructor() throws SomeException{
//some stuff
}

//Case 2
public SomeConstructor() throws SomeException{
//some stuff
throw new SomeException();
}

Case 1- Object initialization can be done, you just need to wrap the instance inside try-catch.
Case 2- Can't happen as you are explicitly throwing an exception.

Hope this helps,

[kevinn lee]

thanks
now I got Ankits point.

[Prithvi Sehgal]

You are welcome mate.

Good luck for SCJP Journey,