How do you reverse using a Comparator?

You can use Comparator. reverseOrder() to have a comparator giving the reverse of the natural ordering. If you want to reverse the ordering of an existing comparator, you can use Comparator. reversed() .

Table of Contents

How do you reverse compare in Java?

The reversed() method of Comparator Interface in Java returns a comparator that imposes the reverse ordering of this comparator. If you use sort method of the array and passes this comparator after applying the reversed method then it will sort the array in reverse order.

What is Comparator reverseOrder?

Comparator reverseOrder() method in Java with examples

The reverseOrder() method of Comparator Interface in Java returns a comparator that use to compare Comparable objects in reverse of natural order. The returned comparator by this method is serializable and throws NullPointerException when comparing null.

How do you sort a list in descending order in Java 8 using Comparator?

3. Using Java 8

Obtain a stream consisting of all elements of the list.
Sort the stream in reverse order using Stream. sorted() method by passing Comparator. reverseOrder() to it that imposes the reverse of the natural ordering.
Collect all elements of sorted stream in a list using Stream. collect() with Collectors.

What does Comparator naturalOrder do?

The naturalOrder() method of Comparator Interface in Java returns a comparator that use to compare Comparable objects in natural order. The returned comparator by this method is serializable and throws NullPointerException when comparing null.

What is Comparator comparing in Java?

Java Comparator interface is used to order the objects of a user-defined class. This interface is found in java. util package and contains 2 methods compare(Object obj1,Object obj2) and equals(Object element).

How do you compare two strings in Java?

Using String. equals() :In Java, string equals() method compares the two given strings based on the data/content of the string. If all the contents of both the strings are same then it returns true. If any character does not match, then it returns false.

How does Comparator work in Java?

Comparator , represents a component that can compare two objects so they can be sorted using sorting functionality in Java. When sorting e.g a Java List you can pass a Java Comparator to the sorting method. The Comparator is then used to compare the objects in the List during sorting.

What does reverseOrder () do in Java?

The reverseOrder() method is used to get a comparator that imposes the reverse of the natural ordering on a collection of objects that implement the Comparable interface.

What is reverseOrder in Java?

The reverseOrder() is a Java Collections class method which returns a comparator that imposes the reverse of the natural ordering on the objects. There is two different types of Java reverseOrder() method which can be differentiated depending on its parameter.

Does Comparator sort ascending or descending?

The default sorting order for an object is ascending order like Integer will be sorted from low to high while descending order is just opposite. Collections. reverseOrder() returns a Comparator which will be used for sorting Objects in descending order.

How do you sort a List in reverse order?

In order to reverse the original order of a list, you can use the reverse() method. The reverse() method is used to reverse the sequence of the list and not to arrange it in a sorted order like the sort() method. reverse() method reverses the sequence of the list permanently.

What does .compare do in Java?

Java String compareTo() Method
The compareTo() method compares two strings lexicographically. The comparison is based on the Unicode value of each character in the strings. The method returns 0 if the string is equal to the other string.

Why do we use Comparator in Java?

Comparator is used in Java to sort objects based on multiple data members (i.e) based on any conditions because Comparable can be used to sort only based on a single data member. Comparator can also be used when we want a sorting order other than the default sorting order of the class.

What is difference between == equals () and compareTo () method?

The equals() tells the equality of two strings whereas the compareTo() method tell how strings are compared lexicographically.

Why use .equals instead of == Java?

We can use == operators for reference comparison (address comparison) and . equals() method for content comparison. In simple words, == checks if both objects point to the same memory location whereas . equals() evaluates to the comparison of values in the objects.

What is difference between Comparator and comparable in Java?

Comparator in Java is used to sort attributes of different objects. Comparable interface compares “this” reference with the object specified. Comparator in Java compares two different class objects provided. Comparable is present in java.

How do you reverse a string array in Java?

Method 3: Code to Reverse String Array in Java

Convert the String Array to the list using Arrays. asList() method.
Reverse the list using Collections.reverse() method.
Convert the list back to the array using list. toArray() method.

What is difference between comparator and comparable in Java?

How do you reverse a list in Java without reverse function?

Example to reverse string in Java by using static method

import java.util.Scanner;
public class ReverseStringExample3.
{
public static void main(String[] arg)
{
ReverseStringExample3 rev=new ReverseStringExample3();
Scanner sc=new Scanner(System.in);
System.out.print(“Enter a string : “);

Is Java sort ascending or descending?

We can sort arrays in ascending order using the sort() method which can be accessed from the Arrays class. The sort() method takes in the array to be sorted as a parameter. To sort an array in descending order, we used the reverseOrder() method provided by the Collections class.

How do you sort in ascending order using Comparator in Java?

There are several ways to sort a list of Objects:

Make the Object implement the Comparable interface and override the compareTo() method. import java.
Pass a Comparator to the Collections. sort() method, which defines how sorting of objects will occur in the list.
Pass lambda expression to Collections.

How do you reverse a list in descending order in Java?

sort() method. This method requires two parameters i.e. the list to be sorted and the Collections. reverseOrder() that reverses the order of an element collection using a Comparator. The ClassCastException is thrown by the Collections.

How do I sort alphabetically in reverse order in Java?

Java Collection Framework provides a convenient reverse comparator, to sort a List of objects in reverse order. You can obtain reverse Comparator, by calling Collections. reverseOrder(), which by default sort List of Integer in reverse numeric order and List of String in reverse alphabetic order.

Can we use == to compare strings in Java?

You should not use == (equality operator) to compare these strings because they compare the reference of the string, i.e. whether they are the same object or not. On the other hand, equals() method compares whether the value of the strings is equal, and not the object itself.

How do you reverse using a Comparator?