convert ArrayList<Object[]> to Object[]

Question

I'm searching for this problem since days and I can't seem to find a proper answer. So I have an ArrayList of Arrays in form of Objects (ArrayList) filled with the result set of a SQL string. My goal is to convert the result of only one row into a one-dimensional Array of Objects.

I have tried several times my research results from this website, but the only knowledge I've made was how to convert a one-dimensional ArrayList to a simple array. I hope you guys can help me in some ways. Thanks!

My table is looking like this:

sizeid | diameter
   1   |    32
   2   |    40

With the SQL-command "SELECT diameter FROM size" I'll get those two numbers 32 and 40, stored in a simple 2x1 table.

|  32  |
|  40  |

Now I want to have them in a one-dimensional Array.

the method to convert:

private Object[] getSizes() {
   query = new SQLquery();
   query.setSQLstring("SELECT diameter FROM size");
   query.runQuery();

   List<Object> sizeList = query.getRowData();
   Object[] sizes = new Object[sizeList.size()];

   // here I want to convert the List to an array..

   return sizes;
}

the method to generate the ArrayList of the class SQLquery:

public void outputResult() {
    try {
       if (result != null) {
          ResultSetMetaData meta = result.getMetaData();
          columns = meta.getColumnCount();
          columnNames = new Object[columns];
          for (int i=1; i<=columnNames.length; i++) {
             columnNames[i-1] = meta.getColumnName(i);
          }
          List<Object> rowData = new ArrayList<Object>();
          while (result.next()) {
            Object[] row = new Object[columns];
            for (int j=0; j<= columns; j++) {
               row[j-1] = result.getString(j);
            }
            rowData.add(row);
         }
      }
   } catch (SQLexception e) {
      System.out.println(e);
   }
}

and the simple get-method of the class SQLquery:

public List<Object> getRowData() {
   return rowData;
}

No, I think he wants an array with all the single-valued results from the query. — Aioros
– Aioros, Commented Apr 18, 2014 at 10:29
eclipse responses me this error message: "type mismatch: cannot convert from Object to Object[]" — user3548416
– user3548416, Commented Apr 18, 2014 at 10:33
Something's wrong here: for (int j=0; j<= columns; j++) row[j-1] = result.getString(j); I believe j should start from 1. — Marko Topolnik
– Marko Topolnik, Commented Apr 18, 2014 at 10:38

Marko Topolnik · Accepted Answer · 2014-04-18 10:37:24Z

1

Apparently, your getRowData() method returns a List<Object> whereas it actually contains arrays. Although this looks strange since you say it always returns a list of arrays, I'll assume that's what you have.

You need a loop which goes over these "objects", downcasting them to Object[], and taking the first member.

Object[] sizes = new Object[sizeList.size()];
int i = 0;
for (Object o : sizeList) sizes[i++] = ((Object[]) o)[0];
return sizes;

answered Apr 18, 2014 at 10:37

Marko Topolnik

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2 Comments

WoDoSc Over a year ago

Why is it strange that the items of the list of objects are arrays? Actually every item of the list of object is representing a resulting row of the SQL query: a row can contain multiple values (the column): this is only a special case where the query selects only one columns, and therefore we have arrays with only one item.

Marko Topolnik Over a year ago

@Nicola It is not strange that the items in the list are arrays. What is strange is that the type of the said list is List<Object>.

Csuki · Accepted Answer · 2014-04-18 10:47:55Z

0

You could use the approach what Marko Topolnik suggested.

However I would suggest to write your own "Table" class, which parses the result set and puts the values into an N*M dimensional array (or List) depending on your query. This way you can store meta information like the size of N or M dimension, etc.

answered Apr 18, 2014 at 10:47

Csuki

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