Dynamically creating objects using a for loop

Question

I'm relatively new to Java and trying to create an application to help with my trading. I have a method to read a csv file that I input, which is table with x number of rows and 3 columns. It reads it as multidimensional String array (String[][]) Eg

Pair----- Buy Price ---Sell Price
AUDUSD 0.9550 --- 0.9386
EURUSD 1.3333 --- 1.3050
GBPUSD 1.5705 --- 1.5550

(please excuse my formatting)

I have a constructor called ForexPair that looks like this:

public class ForexPair extends PriceWarning{

public String pairName;
public double buyPrice;
public double sellPrice;

public ForexPair(String pair, String buy, String sell) {
    pairName = pair;
    buyPrice = Double.valueOf(buy);
    sellPrice = Double.valueOf(sell);
}

My question is this: Can I use a 'for' loop to create an object for each row in my CSV file? I believe I can use an ArrayList for this. However I want the name of each object I create to be the Pair Name in the first column of my csv file. For example:

ForexPair AUDUSD = new ForexPair(pairNames[0], (myArray[0][1]),(myArray[0][2]));

But how do I create the object called AUDUSD using a for loop? So that each object has a different name?

Currently I have this code:

public static void main(String[] args) {

    String[][] myArray = getInputArray();
    String[] pairNames = new String[myArray.length];

    for(int i = 0; i < pairNames.length; i++){
        pairNames[i] = myArray[i][0];                   //Creates 1D String array with pair names.
        ForexPair pairNames[i] = new ForexPair(pairNames[i], (myArray[i][1]),(myArray[i][2]));
    }
}

pairNames is defined as a string array. You cannot redeclare it as a ForexPair in your loop. You need a list of ForexPair, to which you append new instances. "The name of each object" is confusing; you don't need to keep a reference to each object--they're in the list. Edit Oh, you meant a hash--I get it now. — Dave Newton
– Dave Newton, Commented Jun 14, 2013 at 13:51

arshajii · Accepted Answer · 2013-06-14 13:58:53Z

1

Variable names are not relevant - they aren't even kept track of after your code is compiled. If you want to map names to objects you can instead place ForexPair instances in a Map<String, ForexPair>, i.e.

Map<String, ForexPair> map = new HashMap<String, ForexPair>();

...

// in the for-loop:
map.put(pairNames[i], new ForexPair(pairNames[i], myArray[i][1],myArray[i][2]));

Although this seems slightly redundant, as you already have the name as a field in each ForexPair, so you might want to consider removing this field and keeping track of the name only via the map.

edited Jun 14, 2013 at 13:58

answered Jun 14, 2013 at 13:53

arshajii

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Comments

Johannes · Accepted Answer · 2013-06-14 13:54:01Z

0

Yes you can. Use a HashMap.
rough example:

HashMap<String, ForexPair> myMap = new HashMap<String, ForexPair>();
myMap.put("AUDUSD", new ForexPair(pairNames[0], (myArray[0][1]),(myArray[0][2])));
ForexPair pair = myMap.get("AUDUSD");

answered Jun 14, 2013 at 13:54

Johannes

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Comments

PrR3 · Accepted Answer · 2013-06-14 13:58:56Z

0

1.

Can I use a 'for' loop to create an object for each row in my CSV file?

Yes, that's possible:

BufferedReader br = new BufferedReader(new FileReader(yourCsvFile));
String line;
while((line = br.readLine()) != null) {
     // do something with line.
}

2.

But how do I create the object called AUDUSD using a for loop? So that each object has a different name?

I think your mixing up two different concepts: name of variable and value of your variable called pair The value of your variable is the important point, while the name of your variable only provides code quality!

answered Jun 14, 2013 at 13:58

PrR3

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Comments

user2054528 · Accepted Answer · 2013-06-14 14:03:33Z

            final TableLayout tview = (TableLayout) findViewById(R.id.tblGridStructure);
            final JSONArray JarraymenuItems = {item1,it3m1mwer,wer,ds};//your list of items
            for (int i = 0; i < JarraymenuItems.length(); i++) 
                        {
    ableRow tr = new TableRow(this);
        tr.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.WRAP_CONTENT));
                            tview.addView(tr, LayoutParams.FILL_PARENT, 45);
            T
            final TextView etprice = new TextView(this);
            etprice.setText("your text value wat u want to display");
tr.addView(etprice );
int count = tview.getChildCount();
                    if (count % 2 != 0)
                    tr.setBackgroundColor(Color.parseColor("#E3E3E3"));
            }

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