Getting object with max date property from list of objects Java 8
JavaCollectionsJava 8Java Problem Overview
I have a class called Contact
that has a Date lastUpdated;
variable.
I would like to pull the Contact
out of a List<Contact>
that has the max lastUpdated
variable.
I know that this can be done by writing a custom comparator and using Collections.max
, but I was wondering if there is a way this can be done in Java 8 that does not require using a custom comparator, since I just want to pull the one with a max date in just one spot in my code, and the Contact
class should not always use the lastUpdated
variable for comparing instances.
Java Solutions
Solution 1 - Java
Writing custom comparator in Java-8 is very simple. Use:
Comparator.comparing(c -> c.lastUpdated);
So if you have a List<Contact> contacts
, you can use
Contact lastContact = Collections.max(contacts, Comparator.comparing(c -> c.lastUpdated));
Or, using method references:
Contact lastContact = Collections.max(contacts, Comparator.comparing(Contact::getLastUpdated));
Solution 2 - Java
> and the Contact class should not always use the lastUpdated variable > for comparing instances
So you will have to provide a custom comparator whenever you want to compare multiple instances by their lastUpdated
property, as it implies that this class is not comparable by default with this field.
Comparator<Contact> cmp = Comparator.comparing(Contact::getLastUpdated);
As you know you can either use Collections.max
or the Stream API to get the max instance according to this field, but you can't avoid writing a custom comparator.
Solution 3 - Java
Try the following (untested):
contacts.stream().max(Comparator.comparing(Contact::getLastUpdated)).get()
Solution 4 - Java
Use List<T>.stream().max(Comparator<T>).get()
after you defined a suitable Comparator
.
Solution 5 - Java
Since you wanted to do it using java 8 lambdas, use this (assuming you have List<Contact> contacts
):
Contact latest = contacts.stream()
.sorted(Comparator.<Contact, Date>comparing(contact-> contact.getLastUpdated(), Comparator.reverseOrder()))
.findFirst().get();
You can customize this comparator quite easily by simply appending further comparator. So the code is easily modifiable.
List<Contact> sortedContacts = contacts.stream()
.sorted(Comparator.<Contact, Date>comparing(contact-> contact.getLastUpdated(), Comparator.reverseOrder())
.thenComparing(contact -> contact.getAge()))
.collect(Collectors.toList());