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Any Link Between ArrayList and HashMap

Rajendra Prakash
Ranch Hand

Joined: Sep 10, 2009
Posts: 293
Hi Friends, Can you give few interview questions which relates ArrayList and Hashmap. I mean how to link ArrayList and HashMap.
Jesper de Jong
Java Cowboy
Saloon Keeper

Joined: Aug 16, 2005
Posts: 14269
    
  21

I don't know what you mean by "how to link ArrayList and HashMap". Do you mean you want to know what the similarities and differences between these two are?

ArrayList and HashMap are both standard Java collection classes, but they have a different structure and a different purpose. An ArrayList is a an ordered sequence (a list) of objects backed by an array, and a HashMap is an associative array - a data structure that maps keys to values.

See Sun's Collections tutorial and The Collections Framework.

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Rajendra Prakash
Ranch Hand

Joined: Sep 10, 2009
Posts: 293
ArrayList vs HashMap : I have stored objects in ArrayList , can i retrieve same objects in HashMap. is it possible?
Campbell Ritchie
Sheriff

Joined: Oct 13, 2005
Posts: 39409
    
  28
If you put the same objects into the HashMap, then you can retrieve them.

You appear to have misunderstood the two. It is a bit like asking whether you can use a boat or a bicycle. The answer is yes, but where boats work bicycles don't, and vice versa
Rob Spoor
Sheriff

Joined: Oct 27, 2005
Posts: 19720
    
  20

You can put your ArrayList elements in a Map as follows:
The KeyType is usually something immutable like String, Integer or Long. The name of any object is often used. For instance:
Vice versa you have two options:
1) store map.entrySet() in the List
2) ignore the keys and store map.values() in the List.


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