In this article, we’re going to see several examples on how to sort a
List in Java 8.
1. Sort a List of String alphabetically
By purpose, we’ve written London with ‘L’ in low-case to better highlight difference between Comparator.naturalOrder()
that returns a Comparator that sorts by placing capital letters first
and String.CASE_INSENSITIVE_ORDER that returns a case-insensitive
Basically, in Java 7 we were using
Collections.sort() that was accepting a
List and, eventually, a
Comparator - in Java 8 we have the new List.sort() that accepts a
2. Sort a List of Integer
3. Sort a List by String field
Let’s suppose we’ve our
Movie class and we want to sort our
List by title. We can use Comparator.comparing() and pass a function that extracts the field to use for sorting - title - in this example.
The output will be:
As you’ve probably noticed we haven’t passed any
Comparator but the
List is correctly sorted. That’s because of the title - the extracted field - that is a
If you peek at
Comparator.comparing() implementation you will see that it calls
compareTo on the extracted key.
4. Sort a List by double field
In a similar way, we can use Comparator.comparingDouble() for comparing
In the example, we want to order our
Movie by rating, from the highest to the lowest.
We used reversed function on the
Comparator in order to invert default natural-order that is from lowest to highest.
Double.compare() under the hood.
If you need to compare
long you can use
5. Sort a List with custom Comparator
In the previous examples we haven’t specified any
Comparator since it wasn’t necessary but let’s see an example in which we define our own
Movie class has a new field - starred - set using the third constructor parameter. In the example, we want to sort the list so that we have starred movie at the top of the
The result will be:
We can, of course, use Lambda expression instead of
Anonymous class as follows:
And we can also use again
In the latest example
Comparator.comparing() takes as first parameter the function to extract the key to use for sorting and a
Comparator as second parameter.
Comparator uses the extracted keys for comparison,
star2 are indeed
boolean and represents
6. Sort a List with chain of Comparator
In the latest example, we want to have starred movie at the top and then sort by rating.
And the output is:
As you’ve seen we first sort by starred and then by rating - both reversed since we want the highest value and true first.