Question

I have a problem of adding elements into an ArrayList. Each time I do the ‘add’, the entire array content is replaced with the current element value. I end up with eg. 10 repeated element duplicates.

The classes are set up as follows:

public class BradfordReport {
    EmployeeRow _empRow = new EmployeeRow();
    ArrayList<EmployeeRow> _bradfordData = new ArrayList<EmployeeRow>();

    public void Run() {
       // processing to setup Employee row variables
       for (int x=0; x<10; x++) {
           // This next line in debug IS ADJUSTING THE ARRAYLIST DATA!!
           _empRow.EmpNum = x; // etc for other variable in EmployeeRow
           _bradfordData.add(er);
       }
    }
    // THE RESULT IN _bradfordData is 10 elements, all with EmpNum = 10!
 }

public class EmployeeRow {
    int EmpNum;
    string EmpNm; // etc.
 }

Am I getting Java memory allocation confused here? It appears that EmployeeRow variable and the ArrayList are sharing the same memory space – very peculiar. Thanks guys

Answer 1

You are adding the same instance of the EmployeeRow class to the arraylist. Try something like:

public class BradfordReport {
    EmployeeRow _empRow = new EmployeeRow();
    ArrayList<EmployeeRow> _bradfordData = new ArrayList<EmployeeRow>();

    public void Run() {
       // processing to setup Employee row variables
       for (int x=0; x<10; x++) {
           // create a NEW INSTANCE of an EmployeeRow
           _empRow = new EmployeeRow();
           _empRow.EmpNum = x; // etc for other variable in EmployeeRow
           _bradfordData.add(_empRow);
       }
    }
    // THE RESULT IN _bradfordData is 10 elements, all with EmpNum = 10!
}

public class EmployeeRow {
    int EmpNum;
    string EmpNm; // etc.
 }