In Java, the TreeMap class is a sorted map implementation that is based on a red-black tree data structure. It implements the NavigableMap interface and provides a fast and efficient way to store key-value pairs in a sorted order.

Here are some key features of TreeMap:

• TreeMap maintains the order of elements according to their natural ordering (if the keys are Comparable) or according to the custom Comparator provided at the time of creation.

• TreeMap provides O(log n) time complexity for basic operations such as insertion, deletion, and search.

• It does not allow null keys but allows null values.

• TreeMap is not thread-safe. If multiple threads access a TreeMap concurrently and at least one of the threads modifies the map structurally, it must be synchronized externally.

• The TreeMap class provides many methods to navigate and manipulate the map based on the keys, including methods inherited from the NavigableMap interface such as lowerKey(), higherKey(), ceilingEntry(), floorEntry(), etc.

Here is an example of how to create a TreeMap and perform some basic operations:

import java.util.*;

public class TreeMapExample {
    public static void main(String[] args) {
        // Creating a TreeMap
        TreeMap<Integer, String> treeMap = new TreeMap<>();

        // Adding elements to TreeMap
        treeMap.put(2, "Two");
        treeMap.put(1, "One");
        treeMap.put(4, "Four");
        treeMap.put(3, "Three");

        // Displaying TreeMap
        System.out.println("TreeMap: " + treeMap);

        // Accessing values from TreeMap
        System.out.println("Value of key 1: " + treeMap.get(1));

        // Removing elements from TreeMap
        treeMap.remove(2);
        System.out.println("TreeMap after removal of key 2: " + treeMap);

        // Navigating through TreeMap
        System.out.println("First key: " + treeMap.firstKey());
        System.out.println("Last key: " + treeMap.lastKey());
        System.out.println("Key less than 3: " + treeMap.lowerKey(3));
        System.out.println("Key greater than 2: " + treeMap.higherKey(2));
    }
}

Output:

TreeMap: {1=One, 2=Two, 3=Three, 4=Four}
Value of key 1: One
TreeMap after removal of key 2: {1=One, 3=Three, 4=Four}
First key: 1
Last key: 4
Key less than 3: 1
Key greater than 2: 3