Generics and Collection

[Phal Ach]

Hi. I am preparing for SCJP 5. When I give mock exams, I do bad at Generics and Collection. I am not so new to java and I have lots of ArrayList and Vector experience. But I am surely new to java 5. So Generics with collection becomes a bit confusing at times. I have SCJP Study guide(K&B). I need detailed reading on them. Can anybody guide me about that? Thanks

[Rich Raposa]

Make sure you are comfortable with Generics and polymorphism - both with the type of collection and the type of elements. For example, the following statement is valid because ArrayList is a List:

List<Integer> list = new ArrayList<Integer>();

But the following doesn't work, even though a String is obviously an Object:

ArrayList<Object> list = new ArrayList<String>();

This topic is definitely on the exam - not sure how best to learn all the details except maybe by writing some code.

[Phal Ach]

Thanks Rich Raposa. I get your point in the example. That is where I am doing wrong. Can you please tell me which would be best book that gives details about these topics? Thanks again.

[Tejas V Shah]

Hi Phalguni,
Kathey sierra is very nice book for SJCP 5.0 and more about Generics and collections.

Below thing is correct in Array but not correct in collection:

Object a[]=new Integer[5];//correct

consider Parent is super class and Child is sub class or Parent then

List <Parent> list=new ArrayList<Child>();//wrong thing

Cheers,
Tejas

[Phal Ach]

Thanks Tejas.