Java Comparator interface used to sort a array or list of objects based on custom order.Custom ordering of elements is imposed by implementing Comparator.compare() method in the objects.. 1. eg.for descending order just change the positions of a and b in above compare method.In previous articles, we have discussed how to sort list of objects on the basis of single field using Comparable and Comparator interface But, what if we have a requirement to sort ArrayList objects in accordance with more than one fields like firstly sort, according to student name and secondly sort according to student age.Attention reader! acknowledge that you have read and understood our Don’t stop learning now. We learned to sort list and array of objects. Name * Email * Sponsors. By mkyong | Last updated: August 5, 2015. Enter your email address below to join 1000+ fellow learners: Add Comment. Comparator interface is used to order the objects of user-defined classes. We can build one simply, but making use of the Let's take an example of a football team – where we want to line up the players by their rankings.Here, as expected, this results in a compile-time error:Accordingly, in order to be able to sort – we must define our The method returns a number indicating whether the object being compared is less than, equal to, or greater than the object being passed as an argument.Now that we have a clear understanding of natural ordering with If we want a different sorting order, we only need to change the Let's see a quick example of how to use a lambda expression to create a You can explore the Java 8 functionality in-depth in our Hence, despite what we expected, “John” comes before the “Roger” in the sorted collection:To understand more advanced topics of sorting, check out our other articles such as One confusing thing that occasionally happens to me is when my compactor gives me an “IllegalArgumentException: Comparison method violates its general contract!” – while I understand what it happening in the abstract (there’s a situation where A > B > C but A !> C) it can be difficult to find exactly how.Hey Joe – if you can reproduce that in a test, don’t hesitate to open an issue – I’ll be happy to have a look and potentially update the article.We use cookies to improve your experience with the site. One comparator class sorts the employee objects using the age in ascending order and another class sorts the employee objects by the salary in ascending order. Comparable and Comparator. Following function compare obj1 with obj2Suppose we have an array/arraylist of our own class type, containing fields like rollno, name, address, DOB etc and we need to sort the array based on Roll no or name?Method of Collections class for sorting List elements is used to sort the elements of List by the given comparator.By changing the return value in inside compare method you can sort in any order you want. A comparator object is capable of comparing two objects of two different classes. 1. THE unique Spring Security education if you’re working with Java today. Comparator Klasse. Comment. Over the years I have worked with many fortune 500 companies as an eCommerce Architect. In this example, we will show you how to use Java 8 Lambda expression to write a Comparator to sort a List. The Comparable interface that we looked at in the previous section defines a default ordering for the objects of a class.

- Java 8 Lambda : Comparator example. Cancel reply. The java.lang.Comparable and java.util.Comparator are powerful but take time to understand and make use of it, may be it’s due to the lacking of detail example.

Java provides Comparable interface which should be implemented by any custom class if we want to use Arrays or Collections sorting methods.. Popular Examples. If you want to sort the employee objects by age in descending order, you need to change the comparator implementation as given below.As you can see from the output, the Emp objects are now sorted by the age in the descending order.Please let me know if you liked the Java Comparator tutorial with examples in the comments section below.My name is RahimV and I have over 16 years of experience in designing and developing Java applications. For example, if you want to sort the Employee objects by salary in ascending order and by age in descending order? Der Nachteil ist, dass im Endeffekt viele Klassen erstellt werden müssen um alle Möglichkeiten abzudecken. You can have as many Comparator implementations as you want for the given class.As you can see from the output, the Emp objects are sorted by age and salary in the ascending order. We learned how to sort employee objects in java using Comparator interface i.e. Java Comparator interface. Comparator interface in Java is used to define the order of objects of the custom or user defined class.The Java Comparator interface is contained in the java.util package, so you need to import java.util package in order to use the Comparator interface in the code. The canonical reference for building a production grade API with Spring. The Comparable interface that we looked at in the previous section defines a default ordering for the objects of a class.