Generics Generics Generics !!!

[Prav sharma]

List < String > list = new ArrayList();

List list = new ArrayList< String > ();

Which is valid and which is Invalid and why?

[Ankit Garg]

Both are valid. But both will generate a compiler warning. The second one will generate a compilation warning if you try to modify the collection...

[Punit Singh]

Ankit Garg wrote:Both are valid. But both will generate a compiler warning...

I think second one will not generate compiler warning.

[Prav sharma]

Could you please confirm whether 2nd one will generate warning or not?
First one generates.

P.S: I don't have JDK access.

[Ankit Garg]

Punit Singh wrote:

Ankit Garg wrote:Both are valid. But both will generate a compiler warning...

I think second one will not generate compiler warning.

I thought I would correct that before anyone sees it ...

[Punit Singh]

Good one Ankit

[Ankit Garg]

Prav just see this code

import java.util.*;

class WarningTry
{
	public static void main(String[] args)
	{
		List<String> list1 = new ArrayList();  //warning
		List list2 = new ArrayList<String>();
		list1.add("Hello");
		list2.add("Hello");                        //warning
	}
}

[Prav sharma]

Ok

Means 2nd line will generate warning only if we try to add something to it.

If we don't have add for second list then we won't get any warning???

[Punit Singh]

Yes.

[Punit Singh]

Can you think Prav why there is compiler warning in second line add() and why not in first line add() method?
And also

List<String> list1 = new ArrayList(); //warning

why this compiles with warning, while this below one not?

List list2 = new ArrayList<String>();

[Prav sharma]

Is it because that the first declaration tells clearly that Strings can be added Whereas second list is not specifying anything ?

If its like that then what does the RHS of second declaration conveys? Doesn't it serve any purpose?

Punit Singh wrote:Can you think Prav why there is compiler warning in second line add() and why not in first line add() method?
And also

List<String> list1 = new ArrayList(); //warning

why this compiles with warning, while this below one not?

List list2 = new ArrayList<String>();

[Punit Singh]

Prav wrote:If its like that then what does the RHS of second declaration conveys? Doesn't it serve any purpose?

It is serving its purpose na, but in this case it is not deciding what can be added.

Reference type always restricts what you can assign to this reference type, and what can you add if reference type is collection, or what method can be called. This is the power of reference type, RHS is a small child against the power of LHS, LHS says what is possible and what is not always.

List<String> list1 = new ArrayList(); //warning

Here also its reference type is scolding RHS why it is assigning such an ArrayList(), that has no parameter restriction.

[Prav sharma]

Got it

Thanks Guys !!!