java dynamic array creation

Question

I've a situation where i am plotting graph using Aspose library. I created a graph but i hardcoded everything like arrays and column names when filling those arrays. I've given a task to make that process dynamic and read everything from database. I have total record size stored in count variable, which helped me to initialize array of that size. I also have information about number of arrays to be created stored as columnCount. With this information count and columnCount, how can i create arrays since i'll not be hardcoding them now. It will be created inside this block.

for(int i=0; i<columnCount; i++){
       //double type array will be initialized here. each of size count. 
     }

public static void main(String[] args){
    ResultSet rs = ReportHandler.getQueryResult();
    rs.last();
    // get total number of records for array size.
    int count = rs.getRow();
    // this count will tell number of arrays to be created.
    int columnCount = ReportHandler.getCount("035","005");

    // this was static code. now i need to make it dynamic.
     double[] policyYear = new double[count];
     double[] commPremium = new double[count];

     for(int i=0; i<columnCount; i++){
       //double type array will be initialized here. each of size count. 
     }

     rs.beforeFirst();

     int j=0;
     // now i've a result set
     while(rs.next()){
       //static code, need to make it dynamic,
      policyYear[j] = rs.getDouble("policy_year");
      commPremium[j] = rs.getDouble("commulative_premium");
      j++;
  }
}

You don't want while(rs.next()){ inside the for loop. I guess you want the call to next() in the ForUpdate, i.e. j++, rs.next(). — Andy Turner
– Andy Turner, Commented May 23, 2019 at 16:13
You mean you want to dynamically create policyYear, commPremium etc ? In the below answer you mentioned that you know the size, so you can Array or List. But I think your question is different.You need to rephrase your question and explain clearly what you mean by 'make it dynamic' ? — Karthik R
– Karthik R, Commented May 24, 2019 at 6:54
@KarthikR yeah i know size but i don't know number of arrays required. This array creation process should be dynamic. Like policyYear, commPrem arrays is just an example. Next time may be i need more than or less than two arrays for my process. Let me rephrase my question. — Wajeeha Farooqi
– Wajeeha Farooqi, Commented May 24, 2019 at 7:44

DVK · Accepted Answer · 2019-05-23 16:27:15Z

3

If you want to have an array but don't know its size, you can use ArrayList class, which behaves like an array but is dynamically sized.

Use .add() method to add items to your arrays.

UPDATE

As per comment, user needs to have dynamic list of arrays.

So... - use ArrayList of ArrayLists:

ArrayList<ArrayList<Double>> data = new ArrayList<>();
// ....
data.get(colIndex).set(rowIndex, rs.getDouble(colNameByIndex()));
   // assumes get(colIndex) is  not NULL - fix in real code

Or HashMap of ArrayLists

Map<String, ArrayList<Double>> data = new HashMap<>();
// ....
data.get(colName).set(rowIndex, rs.getDouble(colName));
   // assumes get(colName) is  not NULL - fix in real code

edited May 23, 2019 at 16:27

answered May 23, 2019 at 16:14

DVK

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3 Comments

Wajeeha Farooqi Over a year ago

I know its size. i just don't know the number of arrays to be created. previously i declared two arrays (as you can see) but now i need to make it dynamic for my process.

DVK Over a year ago

@WajeehaFarooqi - that wasn't clear from the question

Wajeeha Farooqi Over a year ago

what's columnIndex and rowIndex?? you're referring to the variable j that i've used?

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