Comparators
With the java.util.Comparator interface you can define an ordering for
object instances of a given type. Unlike the java.lang.Comparable interface
which is implemented by the sorted elements itself, Comparators are
external and depending on the use case different orderings can be defined.
Since Java 8
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
public class Comparators {
// There are pre-defined comparators in the Java API:
static Comparator<String> c1 = String.CASE_INSENSITIVE_ORDER;
// The natural ordering can be directly obtained with method references
static Comparator<String> c2 = String::compareTo;
// There is a factory method to compare on attributes
static Comparator<String> c3 = Comparator.comparingInt(String::length);
// Comparators can be reversed and chained
static Comparator<String> c4 = Comparator //
.comparingInt(String::length) //
.reversed() //
.thenComparing(String::compareToIgnoreCase);
// Comparators can be made null safe:
static Comparator<String> c5 = Comparator.nullsFirst(c1);
public static void main(String[] args) {
var input = List.of("apple", "Cherry", "Fig", "Pear", "Mango");
// Sort the list with the different criteria:
System.out.println(input.stream().sorted(c1).toList());
System.out.println(input.stream().sorted(c2).toList());
System.out.println(input.stream().sorted(c3).toList());
System.out.println(input.stream().sorted(c4).toList());
// Sort a list with nulls:
var inputWithNulls = Arrays.asList("c", null, null, "a", "B");
System.out.println(inputWithNulls.stream().sorted(c5).toList());
// Find the minimal element in respect to a Comparator:
System.out.println(Collections.min(input, c4));
}
}
This snippet at GitHub
