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how to store details from file in an object

Medium Priority
Last Modified: 2010-03-31
Hi all,

I have data in a file that I want to store in some kind of object. This file contains lines of data (name, age, gender) like so:

angela 30 female
mike 45 male
danny 20 male
sharon 27 female

What is the best way to store this data, in my view there are two possible options:

1. A list of objects where one line corresponds to one object.

2. One object where which keeps seperate Lists for each field in the file.

What are your thoughts?


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ArrayList<your object>.




An ArrayList of objects?
Allows you to initially ignore the size of the file.




>>Allows you to initially ignore the size of the file

Could you elaborate please?
Assume your class is named Xyz{}

ArrayList<Xyz> data = new ArrayList<Xyz>(initial number of objects reserved);

// Open the file, say to 'input'.

String s;

     while((s = input.readLine()) != null)
           data.add(new Xyz(s));  // Coversions in the constructor of Xyz

// Who cares how many lines the file has.


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Typo:  Coversions -> Conversions


You should consider keeping the type an interface (List<...> [1]).  That way, you can change the implementation later easily.

ArrayList [2] is only one way you can do it, which is backed by an Object array.  You also have choices like LinkedList [3], which uses the good old "link structure" as the back end.  ArrayList is better at random access, and LinkedList is more efficient and constant in size growth.  You might want to look at the javadoc for all implementations and pick the one that suits your needs.

[1] http://java.sun.com/j2se/1.5.0/docs/api/java/util/List.html
[2] http://java.sun.com/j2se/1.5.0/docs/api/java/util/ArrayList.html
[3] http://java.sun.com/j2se/1.5.0/docs/api/java/util/LinkedList.html
Building a list from a file is an operation in one batch.
In that case ArrayList is very efficient.
LinkedList only wins when additions grow over a long time.

Introducing interfaces and the sort comes later.

>> LinkedList only wins when additions grow over a long time.

Also if you remove and insert elements over time.  :)

>> Introducing interfaces and the sort comes later.

Sorry, but I can't agree on that.  People writing java without knowledge on basic concepts of OO like polymorphism gets more dirty code out in the world.  You can say, "this is the idiom for creating new lists":

List<Xyz> data = new ArrayList<Xyz>(initial number of objects reserved);

And have newcomers believe that, and we have one more clean code.  This raises the industry average, and also helps you look after the code these people write.

You might argue that that will risk job security, but you just have to keep ahead in technology.

Anyways, just my opinion.  YMMV.  :)



thanks for all the comments.

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