Tags: Collectors , List , Stream

Collectors.maxBy
This static method from package java.util.stream and class Collectors used to find maximum value from given Collection. This method takes Comparator as an argument.


Source Code

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;

public class CollectorsMaxBy {

    public static void main(String[] args) {
        /* Create and add elements in List of String */
        List listStrings = new ArrayList<String>();
        listStrings.add("Vicky");
        listStrings.add("Carl");
        listStrings.add("Leonard");

        /* Java 8: Use stream over List of String and use `maxBy` with Comparator */
        Optional optionalString = listStrings.stream()
                                             .collect(Collectors.maxBy(new Comparator<String>() {
                                                          public int compare(String str1, String str2) {
                                                               return str1.compareTo(str2);
                                                          }
                                             }));
        /* Check value is available in `Optional` */
        String resultString = optionalString.isPresent() ? optionalString.get() : "No String found";
        /* Print the resultString */
        System.out.println("Maximum String: " + resultString);

        /* Create and add elements in List of Integer */
        List listIntegers = new ArrayList<Integer>();
        listIntegers.add(10);
        listIntegers.add(5);
        listIntegers.add(101);

        /* Java 8: Use stream over List of Integer and use `maxBy` with Comparator */
        Optional optionalInteger = listIntegers.stream()
                                               .collect(Collectors.maxBy(new Comparator<Integer>() {
                                                            public int compare(Integer integer1, Integer integer2) {
                                                                 return integer1 - integer2;
                                                            }
                                               }));
        /* Check value is available in `Optional` */
        Integer resultInteger = optionalInteger.isPresent() ? optionalInteger.get() : 0;
        /* Print the resultInteger */
        System.out.println("Maximum Integer: " + resultInteger);
    }
}

Note: Don't call .get() directly on .collect(Collectors.minBy(new Comparator()) because if there is no element in List then it'll throw an exception java.util.NoSuchElementException: No value present. Always get value in Optional and check isPresent().

Output

Maximum String: Vicky
Maximum Integer: 101

Tags: Collectors , List , Stream