how to sort on a string date on a collection of objects-CodePudding

So I'm having trouble remembering the syntax. I have an List of objects I'm trying to sort based on the value of date. The object looks like this.

Public class someobject{
    private String author;
    private String createDate;
    private String subject;
    private String body;
    private String claimNumber;
    private String authoringDate;
}

I'm trying to sort on the createDate value. Something like

List<someObject> someObjectList = new ArrayList<>();

someObjectList.sort()

currently the way the strings are arriving for the createDate object is YYYY/MM/DD.

CodePudding user response：

Dates in the format YYYY/MM/DD may be correctly sorted as strings, ie lexicographically, so:

someObjectList.sort(Comparator.comparing(someobject::getCreateDate));

or, if you don't have a getter method for createDate:

someObjectList.sort(Comparator.comparing(o -> o.createDate));

CodePudding user response：

For getting the correct comparing result you have to convert String value from the field "creationDate" to Date or LocalDate than you have to make Comparator for instance like that:

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("YYYY/MM/DD");
someObjectList.sort(Comparator.comparingLong(ob -> formatter.parse(ob.createDate).get(ChronoField.EPOCH_DAY)));

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("YYYY/MM/DD");
someObjectList.sort(Comparator.comparingLong(ob -> LocalDate.parse(ob.createDate, formatter).atStartOfDay(ZoneId.systemDefault()).toEpochSecond()));