Use Comparator Methods

Description

In Java 8, new factory methods have been introduced on the Comparator (opens new window) interface to simplify the creation of Comparator objects:

• Comparator.naturalOrder() (opens new window)
• Comparator.reverseOrder() (opens new window)
• Comparator.comparing(keyExtractor) (opens new window)
• Comparator.comparingInt(keyExtractor) (opens new window)
• Comparator.comparingLong(keyExtractor) (opens new window)
• Comparator.comparingDouble(keyExtractor) (opens new window)

This rule replaces complex lambda expressions which represent Comparator instances by simple invocations of one of the methods listed above.

Benefits

Reduces the code clutter and improves the readability.

Tags

Tags

Java 1.8, Lambda, Readability, Coding Conventions, Marker

Code Changes

Natural Order Comparator

Pre

Comparator<User> comparator = (user1, user2) -> user1.compareTo(user2);

Post

Comparator<User> comparator = Comparator.naturalOrder();

Reversed Order Comparator

Pre

Comparator<User> comparator = (user1, user2) -> user2.compareTo(user1);

Post

Comparator<Integer> comparator = Comparator.reverseOrder();

Comparing by a Long Property

Pre

Comparator<User> comparator = (user1, user2) -> user1.getUserId().compareTo(user2.getUserId());

Post

Comparator<User> comparator = Comparator.comparingLong(User::getUserId);

Comparing by a Double Property

Pre

Comparator<User> comparator = (user1, user2) -> user1.getSalary().compareTo(user2.getSalary());

Post

Comparator<User> comparator = Comparator.comparingDouble(User::getSalary);

Comparing by a Comparable Property

Pre

Comparator<User> comparator = (user1, user2) -> user1.getEmail().compareTo(user2.getEmail());

Post

Comparator<User> comparator = Comparator.comparing(User::getEmail);

Creating Reversed Comparator by Property

Pre

Comparator<User> comparator = (user1, user2) -> user2.getAge().compareTo(user1.getAge());

Post

Comparator<User> comparator = Comparator.comparingInt(User::getAge).reversed();

Sorting Collections of Comparables

Pre

users.sort((user1, user2) -> user1.getUserId().compareTo(user2.getUserId()));

Post

users.sort(Comparator.comparingLong(User::getUserId));

🛠️ Auto-refactor Available

You can auto-refactor this with jSparrow.
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Properties

Property	Value
Rule ID	UseComparatorMethods
First seen in jSparrow version	3.23.0
Minimum Java version	1.8
Remediation cost	5 min