Sorting list by an object field missing in some objects in the list

Question

I need to display a list of account objects and sorting on one of the account object fields (all string type). However, some account fields value is null so NOT showing in the JSON. It gives me a null pointer exception when sorting on those missing field. How can I have the Comparator ignore the missing field during sorting ?

I tried Comparator.comparing() but it only works on the common field (existing in all account object). If I tried to sort on the field missing in one of the account objects. NullPointerException happens. Of course, if I tried to force all fields show up with those field as empty string value ("") then it works as normal but it does not look good since it might be too many of those fields.

Accounts definition

@JsonInclude(Include.NON_NULL)
private String type;    
@JsonInclude(Include.NON_NULL)
private String accountNumber;
@JsonInclude(Include.NON_NULL)
private String accountStatus;
@JsonInclude(Include.NON_NULL)
private String accountValue;
    ....

Sort following list - only type and accountNumber are common

"accounts": [
 {
  "type": "type1",
  "accountNumber": "1816227",
  "accountStatus": "cancelled",
 },
 {
  "type": "type2",
  "accountNumber": "2816218",
  "accountValue": "19438.60",

 },
 {
  "type": "type3",
  "accountNumber": "2209890",
  "accountStatus": "inactive",
  "accountValue": "4343.410",
 }

  if (sortField.equalsIgnoreCase("type")) {         
   accountComparator = Comparator.comparing(Accounts::getType);
  }else if(sortField.equalsIgnoreCase("accountNumber")) {
   accountComparator = Comparator.comparing(Accounts::getAccountNumber);
  }else if(sortField.equalsIgnoreCase("accountStatus")) {
   accountComparator = Comparator.comparing(Accounts::getAccountStatus);
  }else if(sortField.equalsIgnoreCase("accountValue")) {    
  accountComparator = Comparator.comparingDouble(acc -> 
    Double.valueOf(acc.getAccountValue()));
   }
   ......

Nullpointer exception on following line when Sort on accountStatus and accountValue which are missing in one of the accounts. totalAcctList.sort(accountComparator.reversed());

As mentioned, if I make all accounts showing accountStatus and accountValue such as "accountStatus":"" and "accountValue":"0.0" then it works.

Mureinik · Accepted Answer · 2019-07-08 05:46:08Z

5

You could decide to have all the nulls at the beginning or the end of the list, and use Comparator.nullsFirst or Comparator.nullsLast respectively:

else if (sortField.equalsIgnoreCase("accountStatus")) {
   accountComparator = 
       Comparator.comparing(Accounts::getAccountStatus, 
                            Comparator.nullsLast(Comparator.naturalOrder()));
}

EDIT:

For accountValue you could take a similar approach, although since primitive doubles can not be null, you'll have to handle them first, before attempting to parse:

else if (sortField.equalsIgnoreCase("accountValue")) {    
  accountComparator = 
      Comparator.comparing((Account a) -> a.getAccountValue() == null)
                .thenComparingDouble((Account a) -> 
                                     Double.parseDouble(a.getAccountValue()));
}

edited Jul 8, 2019 at 5:46

answered Jul 8, 2019 at 5:09

Mureinik

316k54 gold badges400 silver badges405 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

user1747980 Over a year ago

Mureinik, thanks for the great comments. However, it appears that the Comparator.comparingDouble() for sorting on accountValue only have one parameter in the signature.

Mureinik Over a year ago

@user1747980 for doubles, you'll need a slightly different (less elegant) technique. See my edited answer.

Sharon Ben Asher Over a year ago

"primitive doubles can be null" - you need to fix this text

Mureinik Over a year ago

@SharonBenAsher yup, missed the all important "not" there. Thanks for noticing. Edited and fixed.

user1747980 Over a year ago

Thanks Mureinik and Sharon for further improvement of the answer. Mureinik, so a.getAccountValue() == null should be a.getAccountValue() != null , right ?

|

Collectives™ on Stack Overflow

Sorting list by an object field missing in some objects in the list

1 Answer 1

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related