迭代对象列表并比较属性

Question

I am trying to Iterate a list containing Helper class objects and compare the properties of the Helper . Based on the comparison if any validation fails,I wanted to show some error message to user. Below is my code snippet.

public static void main(String[] args) {
    Map<String, String> errorMap = new HashMap<String, String>();
    SimpleDateFormat format = new SimpleDateFormat("dd/MM/yyyy");
    List<HelperDTO> helpers = new HelperTest().getHelpers();

    for (HelperDTO helperDTO : helpers) {
        String helperPkey = helperDTO.getHelperPkey();
        String employeePkey = helperDTO.getEmployeePkey();
        String helperStart = helperDTO.getHelperStart();
        String helperEnd = helperDTO.getHelperEnd();
        if (helperStart == null || "".equals(helperStart)) {
            errorMap.put("helperSt_" + helperPkey,
                    "Helper Start is required");
        }
        if (helperEnd == null || "".equals(helperEnd)) {
            errorMap.put("helperEnd_" + helperPkey,
                    "Helper End is required");
        }
        if (employeePkey == null || "".equals(employeePkey)) {
            errorMap.put("employee_" + helperPkey,
                    "Helper name is required");
        }

        try {
            if (helperStart != null && !"".equals(helperStart)
                    && helperEnd != null && !"".equals(helperEnd)) {

                Date helperStartDate = format.parse(helperStart);
                Date helperEndDate = format.parse(helperEnd);

                if (!helperEndDate.after(helperStartDate)) {
                    errorMap.put("helperEnd_" + helperPkey,
                            "Helper End should be after Helper Start.");
                }
            }

        } catch (ParseException e) {
            e.printStackTrace();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

private List<HelperDTO> getHelpers() {
    List<HelperDTO> hdtoLst = new ArrayList<HelperDTO>();
    hdtoLst.add(new HelperDTO("100", "MANU", "07/06/2013", "08/06/2013"));
    hdtoLst.add(new HelperDTO("101", "DEEPAK", "07/06/2013", "08/06/2013"));
    hdtoLst.add(new HelperDTO("102", "MANU", "07/06/2013", "10/06/2013"));
    return hdtoLst;
        }

How can I compare the endDate of 1st object with the startDate of 2nd object and so on(if the Employee Name is same.In above helper list 1st & 3rd object has same name as 'MANU' ). Can anyone help me on this. Thanks in Advance !!

I don't want to compare the Object or remove the duplicate object from the list .

Answer 1

I think you just need to keep a hash of last seen endDate for each name. Eg declare this before your loop:

Map<String,Date> lastDateForName = new HashMap<String,Date>();

Then after you've tested everything else about the current record, something like this:

if (lastDateForName.get(EmployeePKey) != null
    && !helperStartDate.after(lastDateForName.get(EmployeePKey))) {
  errorMap.put(...);
}
lastDateForName.put(EmployeePKey, helperEndDate)

Answer 2

You can modify your for loop like this :

    for( int i = 0; i < HelperDTO.size(); i++ )
    {
        for( int j = 1; i < HelperDTO.size(); j++ )
        {
            if( HelperDTO.size().get(i).getName.equals(HelperDTO.size().get(j).getName) )
            {
             /* End date of the Current Object */
             Date helperEndDate = format.parse( HelperDTO.get(i).helperEnd );
             /* Start date of the Next Object */
             Date helperStartDate = format.parse( HelperDTO.get(j).helperStart );
            }
        }
    }

Note: I wouldn't advise maintaining another data structure since you are using these dates only once and that too for comparison. The above loop will offer maximum performance both in terms of processing time and memory usage.

Answer 3

Found the way to compare property of list of objects. List helpers = new HelperTest().getHelpers();

    for (int i = 0; i < helpers.size(); i++) {
        String outerPkey = helpers.get(i).getHelperPkey();
        String outerEmpPkey = helpers.get(i).getEmployeePkey();
        String outerStart = helpers.get(i).getHelperStart();
        String outerEnd = helpers.get(i).getHelperEnd();

        if (outerStart == null || "".equals(outerStart)) {
            errorMap.put("helperSt_" + outerPkey,
                    "Helper Start is required");
        }
        if (outerEnd == null || "".equals(outerEnd)) {
            errorMap.put("helperEnd_" + outerPkey, "Helper End is required");
        }
        if (outerEmpPkey == null || "".equals(outerEmpPkey)) {
            errorMap.put("employee_" + outerPkey, "Helper name is required");
        }

        if (compareDate(outerStart, outerEnd)) {
            errorMap.put("helperEnd_" + outerPkey,
                    "Helper End should be after Helper Start.");
        }

        for (int j = 0; j < helpers.size(); j++) {
            String innerEmpPkey = helpers.get(j).getEmployeePkey();
            if (j > i && outerEmpPkey.equals(innerEmpPkey)) {
                String innerStart = helpers.get(j).getHelperStart();
                String innerEnd = helpers.get(j).getHelperEnd();

                if (compareDate(outerStart, outerEnd)
                        || compareDate(innerStart, innerEnd)) {
                    continue;// outer loop should take care this
                }

                if (compareOverlap(innerStart, innerEnd, outerStart,
                        outerEnd)) {
                    errorMap.put("helperEnd_" + outerPkey,
                            "Helper End should be after Helper Start1.");
                }

            }

        }

    }