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DAO method return types

I would like to know about DAO layer. Waht are the return types of those methods. Where, how, why we use this layer. Advantage, disadvantage. I am not clear on this concept. thank in advance
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gudii9
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gudii9
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evedderCommented:
the DAO layer is conceptual you have to define your classes so the type those method returns depends on you, but the idea is to have these classes that act like a pass through your application and the data i mean they are the key to get your info, so you can separate your application logic from the data access. This data can be in a database, text files, etc.
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evedderCommented:
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vakordeCommented:
The concept of layer came into picture to separate the complexity of a particular area. The change in a layer should impact only the adjoining layers.  
If we are talking about DAO, this is built to separate the Database access complexity. There are many different types of databases like CSV file, XML file, Relational, etc. Each of these will have their own mechanism to extract required data. The DAO layer makes sure that even if we changes the database it should not impact the adjoining layer (generally business layer). We just need to do the changes in DAO layer.
To achieve this we must use the POJO objects to communicate data between layers.
To answer your question, the return type should be a POJO. It can be Map, List, String basis on your requirement but it must be a Plain Old Java Object (POJO).
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gudii9Author Commented:
>>>To answer your question, the return type should be a POJO

can we return POJO. How to return a POJO. Can you please point me to simple example
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