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Hashtables and Maps

 
David Dickinson
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Hi All,

I'm confused by how a hashtable works? Is it a spreadsheet style collection where you can store multiple columns of information under a key? Or is it limited to just one column per key?

Ie..

Key, data1, data2, data3

I need a collection which can store a series of data which is related

Thanks
 
juliane gross
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Hi David,

the bad news is,that in a Hashtable you can store one value per one key only.
If you for example put in a value under a same key which was already used, that former key-value-pair will be overwritten by the newly made input.

The good news is, that you do store Objects in Hashtables.
So for example, you coud put in this:


If you need to get back your many things, you just call:


(Don't forget, you always have to cast back your objects to their previous shape.)

An other very cool thing with Hashtables (and their related collection classes) is that you can store in them even whole other classes, interfaces etc. This can be very powerful.
 
It is sorta covered in the JavaRanch Style Guide.
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