The next method takes a function as a parameter, which is applied to the objects being compared by the comparator received as a method parameter. This allows for comparison based on a specific key extracted by the provided function using the comparator received as a method parameter. The method signature looks like this:

Comparatorvs Comparable in Java

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The following methods handle null values appropriately: the first method places null values first, while the last method places them last.

When to use Comparable andComparatorin Java with example

The examples below order Strings. The string class contains one comparator implementation that we can perform case insensitive sort.

The Comparator interface contains only one abstract method, and this method is annotated with @FunctionalInterface and is intended to be implemented with a lambda.

You might find the implementation a bit cumbersome, and you’d be correct. As I previously mentioned, the Comparator interface is a functional interface, allowing us to pass the implementation directly to a sort method. We can also simplify the implementation by leveraging available methods from the Integer class, reducing the implementation itself.

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As you can see, the Comparator interface is highly flexible, allowing for a wide range of operations. Since it is a functional interface, we can implement it inline and chain multiple comparators together, enhancing our code’s readability and functionality. You can sort collections based on various criteria, handle null values gracefully, and combine comparators for more complex sorting logic. This makes the Comparator interface an invaluable tool for developers aiming to write clean, efficient, and maintainable Java code.

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Comparatorexample in Java 8

Comparator comparatorjava

We can even create crazy implementations like this to sort by object multiple fields, although I don't recommend doing it so because they are too verbose and cumbersome.

I commented out this method implementation that doesn’t use a Comparator, so you can see the difference. By adjusting the chain sequence, we can change the order of priority. In this example, the sort will be performed first on the cashback field, then on the createdAt field, and so on.

Comparator comparatorw3schools

In the test below, I combined two comparators to sort a collection. The collection is first ordered by the cashBack field and then by the createdAt field.

Before diving into this tutorial, I highly recommend reading my previous tutorial on the Comparable interface. To be proficient in sorting in Java, it is essential to understand both the Comparable and Comparator interfaces and know when to use each one.

We can chain methods from the Comparator interface to enhance code readability and conciseness. By creating a class that implements the Comparable interface, we can utilize the Comparator interface methods within the compare method implementation as follows:

This method allows you to combine two comparators. First, it compares two objects using the comparator it’s called on. If the first comparator considers the objects equal (returns 0), then the second comparator, provided as a parameter, is used. This approach enables chaining comparators to compare objects by multiple fields.

By using these interfaces appropriately, you can effectively manage and customize the ordering of objects in your Java applications.

Comparator comparatorexample

Let's start with the first method, called reversed(). This method can be called on a comparator to, as you guessed, reverse the order of sorting. Essentially, it converts this:

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This interface includes several static and default methods, which I will cover later in this tutorial. Please bear with me.

For example, we could use it to sort collections by the day of the week because the day of the week is an Integer. Hence, we can apply thenComparingToInt method.

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The reverseOrder method, as the name suggests, reverses the order of a sort, and it has the same functionality as the reversed default method. The naturalOrder method defines a natural sort order. The reverseOrder is the opposite of the naturalOrder method.

ComparatorMinecraft

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Comparatorin Java

Java’s official documentation doesn’t specify the exact positive and negative integers that must be returned from the compareTo method. The numbers 1 and -1 are used as examples, though many standard Java implementations, such as the Integer class, commonly use these values. As you can see, the contract is similar to the Comparable.compareTo()

I am a Java Developer | OCA Java EE 8 | Spring Professional | AWS CDA | CKA | DCA | Oracle DB CA. I started programming at age 34 and still learning.

To demonstrate the use of the Comparator interface, let me define an example class. This simple POJO (Plain Old Java Object) class represents a purchase transaction. It contains several fields that we can use to compare and eventually sort objects instantiated from this class.

The thenComparing method has two overloaded methods that follow the same approach. First, it compares two objects using the comparator it’s called on. If the first comparator considers the objects equal (returns 0), then the second comparator, provided as a parameter, is used.

As you can see, I pass it as an argument to the Collection.sort() method. As a result, we will have a collection sorted by cashback from the lower value to the higher one.

Thank you for reading! If you enjoyed this post, please like and follow it. If you have any questions or suggestions, feel free to leave a comment or connect with me on my LinkedIn account.

Imagine we need to sort a collection by the day of the week derived from the createdAt field. To achieve this, we pass a function to the comparator that extracts the day of the week from the createdAt field, which will then be used during the secondary comparison.

In addition to the default methods that can be called on a comparator, there are static methods that can be used without an existing comparator instance.

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Most likely, you will use Comparator inline implementation within a stream. In this chapter, I will provide some examples to illustrate its usage.

The Comparator interface provides two versions of the comparing method. The first version accepts a function and a comparator. It applies the function to objects for comparison and then compares them.

This tutorial contains many code examples. Some of those examples have repeated code that can be optimized. I did this on purpose because it will better explain how it works.