What is Comparator.comparingInt method in Java?

comparingInt is a static method of the Comparator that sorts a list of elements of any type using an integer sort key. The sort key is extracted with the help of the ToIntFunction functional interface, whose implementation is passed as a parameter to the method.

Syntax

public static <T> Comparator<T> comparingInt(ToIntFunction<? super T> keyExtractor)

Parameters

ToIntFunction<? super T> keyExtractor: Function to extract the sort key.

Return value

The method returns a Comparator.

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
public class Main1 {
    static class Packet{
        int size;
        public Packet(int size) {
            this.size = size;
        }
        @Override
        public String toString() {
            return "Packet{" +
                    "size=" + size +
                    '}';
        }
    }
    public static void main(String[] args) {
        List<Packet> packetList = Arrays.asList(new Packet(4), new Packet(10), new Packet(2));
        System.out.println("Before sorting: " + packetList);
        packetList.sort(Comparator.comparingInt(packet -> packet.size));
        System.out.println("After sorting: " + packetList);
    }
}

Explanation

In lines 1-3, we import the relevant packages.
In line 7, we define a Packet class with size as the attribute.
In line 23, we create a list of different Packet objects with different sizes.
In line 24, we print the list of Packet objects created before sorting.
In line 25, we sort the list using the comparingInt method, where we create an implementation of the ToIntFunction interface that extracts the size attribute from the Packet objects.
In line 26, we print the list of Packet objects after sorting.

What is Comparator.comparingInt method in Java?

Syntax

Parameters

Return value

Code

Explanation