File APIs for Java Developers
Manipulate DOC, XLS, PPT, PDF and many others from your application.
The moose likes Programmer Certification (SCJP/OCPJP) and the fly likes Doubt in generics..please help.. Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login
JavaRanch » Java Forums » Certification » Programmer Certification (SCJP/OCPJP)
Bookmark "Doubt in generics..please help.." Watch "Doubt in generics..please help.." New topic

Doubt in generics..please help..

Manpreet Kaur

Joined: Jul 03, 2008
Posts: 8
The following question is from

public class Gen<G>
G g;
Gen(G g)
this.g =g;
public static void main(String[] args)
Gen<String> arr[] = new Gen[5]; //line 1
arr[0] = new Gen("Java"); //line 2
arr[1] = new Gen(1); //line 3
arr[2] = (Gen<String> new Gen(1); //line 4
arr[3] = (Gen<String> new Gen<Integer>(1); //line 5
for(Gen o:arr)

The options are
a)Compile time Error at line 1
b)Compile time Error at line 3
c)Compile time Error at line 4
d)Compile time Error at line 5
e)Run Time Error


3) d.
We can cast raw type to specific type but we cannot type cast Integer type to String type

My question is why does not compiler give an error on line 3 when we are trying to add and int value to a type-safe String.

Please help.


[ July 09, 2008: Message edited by: Manpreet Kaur ]
[ July 09, 2008: Message edited by: Manpreet Kaur ]
Raphael Rabadan
Ranch Hand

Joined: Jul 05, 2008
Posts: 141

on line 3 you will only have a warning of safety because you arent using any parameter to the raw type.
So, it should give an error if it was like since its not, will just pass.

SCJP Java 6 (98%) - Story, SCJA (88%) - Story
Soroj Margun
Ranch Hand

Joined: Jun 15, 2008
Posts: 44
Hi Manpreet,

You're already answer yourseft.

We can cast raw type to specific type

Object is still raw type unless you explicit specify it to be a generic type. On the other hand, all generic type is also put raw type. Do not forget this for your SCJP.

SCJP 1.2; SCWCD 1.2,1.4; SCBCD 1.3; SCJD 5.0
Nabila Mohammad
Ranch Hand

Joined: Nov 05, 2007
Posts: 661
Can some one please elaborate on what's the "RAw type"?

The future belongs to those who believe in the beauty of their dreams.Dream BIG!
I agree. Here's the link:
subject: Doubt in generics..please help..
jQuery in Action, 3rd edition