Generic quiz

[Bob CHOI]

My code below,

import java.util.*;
 
class Mixed {
 
public static void main(String[] args) {
 
Object o = new Object();
List<Object> typeSafe = new ArrayList<Object>();//1
List typeUnSafe = new ArrayList();//2
 
typeSafe = typeUnSafe;//3
typeSafe.add(o);//4
typeSafe.get(0);//5
typeSafe.remove(0);//6
typeUnSafe = typeSafe;//7
typeUnSafe.add(o);//8
typeUnSafe.get(0);//9
typeUnSafe.remove(0);//10
 
}
 
}

Which lines produce compilation warnings, and why? :roll:
[ December 18, 2006: Message edited by: Bob CHOI ]

[Pinkal Patel]

    
 
[B]typeSafe = typeUnSafe; //3[/B] [I]//unchecked conversion[/I]
 
and 
 
[B]typeUnSafe.add(o); //8[/B] [I]//unchecked conversion[/I]

Will Gave Warning

Pls find Couase in Italics format

[Sanjeev Singh]

//1 # NO PROBLEM- A typed collection of type object is declared.
//2 # NO PROBLEM- A untyped collection is declared.
//3 # PROBLEM- A typed reference is being forced to refer to a collection which is not typed and can take any element... so warning for refering a possible currupted collection.
//4 # NO PROBLEM-element of type Object is added in collection of type Object.
//5 # NO PROBLEM-no collection modification.
//6 # NO PROBLEM-no collection modification.
//7 # NO PROBLEM - Unsafe collection can refer any type of collection.
//8 # PROBLEM-There is always a warning when we use a non-typed collection to add a element.
//9 # NO PROBLEM-no collection modification.
//10 # NO PROBLEM-no collection modification.

[Burkhard Hassel]

more about line 4:
an object is added to an <Object> list.
Adding to a parameterized collection never produces a warning. Either it compiles (type OK) or not (type not OK).

Only reference type counts:
The variable is generic, it doesn't matter that the object (the ArrayList) is non-generic. You can safely put objects in "typeSafe". We have been already warned (that the ArrayList "typeSafe" refers to is non-generic) in line three.


Yours,
Bu.

[Bob CHOI]

Warning on unchecked conversion,

- when generic collection varaible is referred to non-generic collection instance

- when non-generic collection varaible is used to invoke generic parameterized method

"simple" enough