How to Convert one type of Collection object data's to Another Collection Object

[Bubesh Sankar]

Hi Friends,

1.we know that LinkedList is faster than ARRAYLIST on insertion and deletion,For iterating to get data inside object arraylist is faster. Is it possible to use Linked list for insertion after how to convert that object to arraylist for iterating and then to Linked list for deletion? please send me some sample code....

2. How to convert a array details to arraylist and then reverse...

[Ilja Preuss]

1.

An ArrayList is *not* faster for iteration, only for *random access*.

You cannot really "convert" one type of list to another. What you can do is creating a new list with the elements of the old. Whether that's worth it depends on your usage scenario, of course.

Do you actually have a performance problem?

2.

Take a look at Arrays.asList and Collection.toArray

[Paul Sturrock]

Not an advanced question. Moving...

[Ådne Brunborg]

You can only convert (as in "cast") between objects if "instanceof" is true. So, you can convert from ArrayList to List, and from LinkedList to List (since both ArrayList and LinkedList "is-a" List), but you cannot cast from ArrayList to LinkedList.

Now, as to performance differences - it is fair to say that in such cases that you would get a performance improvement on the actual insert/delete and iterate operations, you would lose it when you start converting between List implementations, or going back and forth between Lists and arrays.

But, if you really want to, there is addAll:

List myLinkedList = new LinkedList();
//do LinkedList stuff
List myArrayList = new ArrayList();
myArrayList.addAll(myLinkedList);
//do ArrayList suff
    

The bottom line? Choose the implementation you think will be best for the specific case, and stick with it.
[ November 15, 2006: Message edited by: �dne Brunborg ]

[Stan James]

There might be a case for creating one collection and then populating another, such as loading a large unordered Set and then sorting it all at once by adding it to a TreeSet. I'd want to see comparisons on real data to prove it's worth while.

[Ilja Preuss]

Originally posted by Stan James:
There might be a case for creating one collection and then populating another, such as loading a large unordered Set and then sorting it all at once by adding it to a TreeSet. I'd want to see comparisons on real data to prove it's worth while.

If I remember correctly, a TreeSet *cannot* possibly sort them all at once - the whole algorithm is based on element-by-element insertion.

[Ilja Preuss]

Originally posted by �dne Brunborg:
You can only convert (as in "cast") between objects if "instanceof" is true. So, you can convert from ArrayList to List, and from LinkedList to List (since both ArrayList and LinkedList "is-a" List), but you cannot cast from ArrayList to LinkedList.

Note that this actually doesn't convert the object, but just the type of the reference.