NavigableMap Interface in Java – Guide with Examples

public interface NavigableMap<K, V> extends SortedMap<K, V>

Map
 └─ SortedMap
     └─ NavigableMap
         ├─ TreeMap
         └─ ConcurrentNavigableMap
             └─ ConcurrentSkipListMap

import java.time.LocalDate;
import java.util.NavigableMap;
import java.util.TreeMap;

public class RateOnDate {
    public static void main(String[] args) {
        // Date a new interest rate starts -> rate in %
        NavigableMap<LocalDate, Double> rates = new TreeMap<>();
        rates.put(LocalDate.of(2024, 1, 1), 6.5);
        rates.put(LocalDate.of(2024, 7, 1), 6.25);
        rates.put(LocalDate.of(2025, 2, 15), 6.0);

        for (LocalDate d : new LocalDate[] {
                LocalDate.of(2024, 3, 10), LocalDate.of(2024, 7, 1), LocalDate.of(2025, 6, 30), LocalDate.of(2023, 12, 31)}) {
            var entry = rates.floorEntry(d);          // the latest change on or before d
            System.out.println(d + " -> " + (entry == null ? "no rate yet" : entry.getValue() + "% (since " + entry.getKey() + ")"));
        }
    }
}

import java.util.NavigableMap;
import java.util.TreeMap;

public class NavigableMapMethods {
    public static void main(String[] args) {
        NavigableMap<Integer, String> floors = new TreeMap<>();
        floors.put(0, "Lobby");
        floors.put(2, "Cafe");
        floors.put(5, "Offices");
        floors.put(8, "Gym");
        floors.put(10, "Roof");

        System.out.println("lowerKey(5):    " + floors.lowerKey(5));
        System.out.println("floorEntry(6):  " + floors.floorEntry(6));
        System.out.println("ceilingKey(6):  " + floors.ceilingKey(6));
        System.out.println("higherEntry(8): " + floors.higherEntry(8));

        System.out.println("headMap(5, true):           " + floors.headMap(5, true));
        System.out.println("tailMap(5, false):          " + floors.tailMap(5, false));
        System.out.println("subMap(2, true, 8, true):   " + floors.subMap(2, true, 8, true));
        System.out.println("descendingMap():            " + floors.descendingMap());
        System.out.println("descendingKeySet():         " + floors.descendingKeySet());
        System.out.println("navigableKeySet().floor(7): " + floors.navigableKeySet().floor(7));
    }
}

import java.util.Map;
import java.util.NavigableMap;
import java.util.TreeMap;

public class ScheduledJobs {
    public static void main(String[] args) {
        NavigableMap<Integer, String> jobs = new TreeMap<>();   // run time (minute of day) -> job
        jobs.put(540, "send reports");
        jobs.put(60, "backup database");
        jobs.put(720, "clear cache");
        jobs.put(300, "rotate logs");

        int now = 600;
        System.out.println("Jobs due by minute " + now + ":");
        Map.Entry<Integer, String> next;
        while ((next = jobs.firstEntry()) != null && next.getKey() <= now) {
            jobs.pollFirstEntry();                                // remove it as we run it
            System.out.println("  running " + next.getValue() + " (scheduled at " + next.getKey() + ")");
        }
        System.out.println("Still waiting: " + jobs);
    }
}

import java.util.concurrent.ConcurrentNavigableMap;
import java.util.concurrent.ConcurrentSkipListMap;

public class ConcurrentSortedMap {
    public static void main(String[] args) throws InterruptedException {
        ConcurrentNavigableMap<Integer, String> orders = new ConcurrentSkipListMap<>();

        Thread a = new Thread(() -> { for (int i = 1; i <= 500; i += 2) orders.put(i, "A"); });
        Thread b = new Thread(() -> { for (int i = 2; i <= 500; i += 2) orders.put(i, "B"); });
        a.start(); b.start();
        a.join();  b.join();

        System.out.println("size=" + orders.size() + ", firstKey=" + orders.firstKey() + ", lastKey=" + orders.lastKey());
        System.out.println("headMap(4): " + orders.headMap(4));
        System.out.println("ceilingKey(250): " + orders.ceilingKey(250));
    }
}