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Creating a hash of objects
Fundamental classes example from a Well House Consultants training course
More on Fundamental classes [link]

This example is described in the following article(s):
   • Java - factory method, encapsulation, hashmap example - [link]

Source code: AUtil.java Module: J714
This example puts together various Java elements into a complete program to set up a table, keyed by a text string,
of objects. We've used a "Hashmap" from the Java Utility Package to hold our keys and the objects which we've
associated with each key - in this case railway station information keyed by the industry's internal three letter
code system. You'll note that there's no detail of what the data format of the incoming data file is in this
main application, as that minutiae is delegated down to the NetworkStation class, which will be written and
maitaineed by an expert in that particular data, and can be shared between a number of different applications all of
which need to access that data.

import java.io.*;
import java.util.*;

public class AUtil{
public static void main(String [] args) throws IOException {

// We're going to read the incoming data file defined on the comment line, one line at a time

        BufferedReader Stuff = new BufferedReader(new FileReader(args[0]));

        String lyne;
        HashMap info = new HashMap();

// Loop through the incoming lines of data and pass each to a factory to return a NetworkStation object
        while ( (lyne = Stuff.readLine()) != null) {
                NetworkStation current = (NetworkStation)NetworkStation.Factory(lyne);
                // We've assumed that the factory always succeeds. May want to check for null return?
                String ThreeLetterCode = current.getCode();
                // add the object newly manufactured by the factory into the hash

// For testing, output the object that has the key "LLS" as converted to a string


// Iterate through the hash ... in other words output all the objects

        Set Places = info.keySet();
        Iterator Place = Places.iterator();

        while(Place.hasNext()) {
                String TLC = (String)Place.next();


Learn about this subject
This module and example are covered on the following public courses:
 * Learning to Program in Java
 * Java Bootcamp
 * Java Programming for the Web
Also available on on site courses for larger groups

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Other Examples
This example comes from our "Fundamental classes" training module. You'll find a description of the topic and some other closely related examples on the "Fundamental classes" module index page.

Full description of the source code
You can learn more about this example on the training courses listed on this page, on which you'll be given a full set of training notes.

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Other resources
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