It returns in constant time, but youll pay the (small) overhead of the view for each operation. Guavas Lists.reverse returns a view of the list that is reversed. Java Program to sort an ArrayList using Comparator import java.util. Collections.reverse takes a mutable list and reverses its order. You can see your Comparator implementation has become quite simple and you can write them in just one line. By default, the sort () method sorts the elements in ascending order. The Collections.sort () method helps us to sort the elements available in the specified list of Collections. Though, you can use Collection.sort() if you are not using JDK 8, just replace the List.sort() with Collections.sort() and the program should work fine.Īlso, I have used the lambda expression to implement our Comparators as oppose to the Anonymous class which we used earlier. reverseOrder () 1) sort () The Collections.sort () method is available in the class. I have also used the new List.sort() method of JDK 8 for sorting. In this article, I have created two implementations of interface, one called TitleComparator, which sorts the list of courses on their title and other, called FeeComparator which sorts the list of courses on their price. Here is our Java program which will sort the list of courses using custom comparators. Java Program to Sort an ArrayList of Objects by Fields using Comparator I have a domain object called Course, which contains the title and price of the course, a title is a String and the fee is long value. In this article, I'll show you how to sort a List of objects in both ascending and descending order by using Comparator. How to Sort an ArrayList of Objects by Fields or Properties using Comparator You can further see these Java 8 Tutorials and courses to learn more about new methods added on the Comparator and List interface to make sorting easier in Java 8. The List.sort() of Java 8 will then sort the list on order imposed by Comparable. This method accepts a Comparator and sorts elements based upon that, but if you want to sort on the natural order, just don't supply a Comparator and pass null. This is similar to Collections.sort() and you can use it to sort a list of objects using both Comparator and Comparable. the JDK 8 release also added a couple of methods on both class and to make sorting easier.įor example, you can also use List.sort() method to sort a List of objects. If you want you can use Comparable to sort in the natural order and in the decreasing order of natural order imposed by Comparator. The JDK API provides another convenient method Collections.reverseOrder(Comparator c) which returns a comparator with the opposite order of the given Comparator.ītw, this is not the only way to sort an ArrayList of objects in Java. Public static void main(String.This method is a good example of a strategy pattern because it uses the Comparator you provide to sort your objects, which means you can sort the same list of objects into different order by just changing the Comparator.įor example, You can sort an ArrayList of Objects in descending order by just reversing the order of your Comparator. I have created a list of files from a directory, which I display unsorted, sorted and reverse sorted using a simple Comparator for the sort and then calling reversed() on it to get the reversed version of that Comparator. This can easily be done using Java 8 and the use of a reversed Comparator.
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