I have a POJO looking like this:
public class Pojo implements Comparable<Pojo> {
private String type;
private String journalId;
private Date bookingDate;
private Long account;
private String description;
private BigDecimal debit;
private BigDecimal credit;
....
}
and I want to sort a list of these POJOs. Currently my compareTo
method looks like this:
@Override
public int compareTo(EfdisJournal other) {
int i = this.type.compareTo(other.type);
if (i != 0)
return i;
if (this.bookingDate != null && other.bookingDate != null)
i = this.bookingDate.compareTo(other.bookingDate);
if (i != 0)
return i;
if (this.journalId != null && other.journalId != null)
i = this.journalId.compareTo(other.journalId);
if (i != 0)
return i;
return this.account.compareTo(other.account);
}
If I run a sort with this compareTo
method, I get this java.lang.IllegalArgumentException: Comparison method violates its general contract
error. I did google a bit and I think it happens because some of the fields are null
on comparison. Yet I have no idea how to solve this or if I am right why that error appears.
The comparison should work like this: 1st compare by type
, then compare by bookingDate
, as 3rd compare by journalId
and at last compare by account
. All comparisons should be ascending.
type
is never nullbookingDate
may be nulljournalId
may be nullaccount
is never nullEDIT:
Sadly I was not able to implement the method, so that the order is as needed. Yet, i solved the problem I had, because the stored procedure yielded 2 resultsets, of which the second was order as needed, so the only thing I had to do was to use the 2nd resultset instead of the first.
You need to deal with the case where one instance has a null bookingDate
, and the other has a non-null bookingDate
.
You should decide whether things with null bookingDate
should be sorted before or after things with a non-null bookingDate
, and write your compareTo appropriately. (And then journalId
too.) Then you can get an order that sorts consistently.
For instance:
@Override
public int compareTo(EfdisJournal other) {
int i = this.type.compareTo(other.type);
if (i != 0) {
return i;
}
if ((this.bookingDate==null) ^ (other.bookingDate==null)) {
return (this.bookingDate==null ? -1 : 1);
}
if (this.bookingDate != null && other.bookingDate != null) {
i = this.bookingDate.compareTo(other.bookingDate);
}
if (i != 0) {
return i;
}
if ((this.journalId==null) ^ (other.journalId==null)) {
return (this.journalId==null ? -1 : 1);
}
if (this.journalId != null && other.journalId != null) {
i = this.journalId.compareTo(other.journalId);
}
if (i != 0) {
return i;
}
return this.account.compareTo(other.account);
}