Combining attributes in a class

I have the following custom class

class rollingD {
private String settDate;
private String publishingPeriodCommencingTime;
private String fuelTypeGeneration;
public String getSettDate() {
return settDate;
}
public void setSettDate(String settDate) {
this.settDate = settDate;
}
public String getPublishingPeriodCommencingTime() {
return publishingPeriodCommencingTime;
}
public void setPublishingPeriodCommencingTime(String publishingPeriodCommencingTime) {
this.publishingPeriodCommencingTime = publishingPeriodCommencingTime ;
}
public String getFuelTypeGeneration() {
return fuelTypeGeneration;
}
public void setFuelTypeGeneration(String fuelTypeGeneration) {
this.fuelTypeGeneration = fuelTypeGeneration;
}
@Override
public String toString() {
return String.format("%s,%s,%s",
settDate,
publishingPeriodCommencingTime,
fuelTypeGeneration);
}} 

The items add to my array list as below

ArrayList<rollingD> aList = new ArrayList<>();

The attributes

settDate
and 
publishingPeriodCommencingTime

are separate entities

01/04/2020
and 
21:34:26

What i would like to do is within my class i want to combine my attributes before adding them to the array list

so i would end up with

01/04/2020 21:34:26  

as a single attribute

I would therefore only have 2 attributes in my arraylist which i can then sort etc

Can someone provide assistance please.

I have tried streaming a map afterwards and combining the streams after but i realised that is not an ideal solution as i need to then work with the arraylist further down the line and ideally with datetimestamp and the value as my only two items

This is the code for parsing the API

      while(parser.hasNext()) {
XMLEvent event = parser.nextEvent();
switch(event.getEventType()) {
case XMLStreamConstants.START_ELEMENT:
StartElement startElement = event.asStartElement();
String qName = startElement.getName().getLocalPart();
if (qName.equalsIgnoreCase("settDate")) {
rD = new rollingD(null,null,null);
bMarks = true;
} else if (qName.equalsIgnoreCase("publishingPeriodCommencingTime")) {
bLastName = true;
} else if (qName.equalsIgnoreCase("fuelTypeGeneration")) {
bNickName = true;
aList.add(rD);
}
break;
case XMLStreamConstants.CHARACTERS:
Characters characters = event.asCharacters();
if(bMarks) {
//  System.out.println("settDate: " + characters.getData());
rD.getTimeStamp(characters.getData(),null,null);
bMarks = false;
}
if(bLastName) {
//  System.out.println("publishingPeriodCommencingTime: " + characters.getData());
rD.getTimeStamp(null,characters.getData(),null);
bLastName = false;
}
if(bNickName) {
// System.out.println("fuelTypeGeneration: " + characters.getData());
rD.getTimeStamp(null,null,characters.getData());
bNickName = false;
}
break;
case XMLStreamConstants.END_ELEMENT:
EndElement endElement = event.asEndElement();
//List<String> namesList = aList.stream()
//.map(x->x.getSettDate()+" "+ x.getPublishingPeriodCommencingTime()+","+ x.getFuelTypeGeneration())
//.collect(Collectors.toList());
//Collections.sort(namesList);
//
//for (String name : namesList) {
//System.out.println(name);
//}
if(endElement.getName().getLocalPart().equalsIgnoreCase("item")) {
System.out.println();
}
break;
} 
}  

Do it as follows:

class RollingD {
private String settDate;
private String publishingPeriodCommencingTime;
private String fuelTypeGeneration;
private String timeStamp;
public RollingD(String settDate, String publishingPeriodCommencingTime, String fuelTypeGeneration) {
this.settDate = settDate;
this.publishingPeriodCommencingTime = publishingPeriodCommencingTime;
this.fuelTypeGeneration = fuelTypeGeneration;
timeStamp = settDate != null && publishingPeriodCommencingTime != null && !settDate.isEmpty()
&& !publishingPeriodCommencingTime.isEmpty() ? settDate + " " + publishingPeriodCommencingTime : "";
}
public String getTimeStamp() {
return settDate != null && publishingPeriodCommencingTime != null && !settDate.isEmpty()
&& !publishingPeriodCommencingTime.isEmpty() ? settDate + " " + publishingPeriodCommencingTime : "";
}
// ..Do not create any setter for timeStamp
// ..Other getters and setters
@Override
public String toString() {
return "RollingD [settDate=" + settDate + ", publishingPeriodCommencingTime=" + publishingPeriodCommencingTime
+ ", fuelTypeGeneration=" + fuelTypeGeneration + ", timeStamp=" + timeStamp + "]";
}
}

Demo:

public class Main {
public static void main(String[] args) {
RollingD rd1 = new RollingD("", "", "G");
System.out.println(rd1);
RollingD rd2 = new RollingD("01/04/2020", "", "G");
System.out.println(rd2);
RollingD rd3 = new RollingD("", "21:34:26", "G");
System.out.println(rd3);
RollingD rd4 = new RollingD("01/04/2020", "21:34:26", "G");
System.out.println(rd4);
}
}

Output:

RollingD [settDate=, publishingPeriodCommencingTime=, fuelTypeGeneration=G, timeStamp=]
RollingD [settDate=01/04/2020, publishingPeriodCommencingTime=, fuelTypeGeneration=G, timeStamp=]
RollingD [settDate=, publishingPeriodCommencingTime=21:34:26, fuelTypeGeneration=G, timeStamp=]
RollingD [settDate=01/04/2020, publishingPeriodCommencingTime=21:34:26, fuelTypeGeneration=G, timeStamp=01/04/2020 21:34:26]

The are some miss-concepts on your approach.
<br>Do not need to do any combinations of parameters inside base object(or before adding to).
<br>Just added as you did the objects on List Data Structure
<br>Your issues is maybe: How to process further the list, based on stored-objects
properties.(eg: sorting based on names, date_hours,etc)
<br>Here I strongly advise to search on List methods capabilities.(using a comparator, etc)