TreeMap in Java

In Java, TreeMap is an implementation of the NavigableMap interface and it is used to store key-value pairs in a sorted order. It uses a red-black tree as the underlying data structure to maintain the keys in sorted order. Here’s an overview of TreeMap in Java along with some examples.

Creating a TreeMap

You can create a new TreeMap object using one of the following constructors:

// Creates an empty TreeMap with natural ordering
TreeMap<K, V> map1 = new TreeMap<>();

// Creates an empty TreeMap with a custom Comparator
TreeMap<K, V> map2 = new TreeMap<>(Comparator<? super K> comparator);

// Creates a TreeMap with the same mappings as the given map
TreeMap<K, V> map3 = new TreeMap<>(Map<? extends K, ? extends V> map);

Adding and Retrieving Elements

To add elements to the TreeMap, you can use the put() method, which takes a key and a value:

// Creating a TreeMap with natural ordering
TreeMap<Integer, String> map = new TreeMap<>();
map.put(1, "One");
map.put(3, "Three");
map.put(2, "Two");

To retrieve a value from the TreeMap, you can use the get() method, which takes a key and returns the associated value:

String value = map.get(2); // value is "Two"

Removing Elements

To remove an element from the TreeMap, you can use the remove() method, which takes a key and removes the associated key-value pair:

map.remove(2); // removes the key-value pair with key 2

Iterating over TreeMap

You can use a for-each loop to iterate over the entries of a TreeMap:

for (Map.Entry<Integer, String> entry : map.entrySet()) {
    int key = entry.getKey();
    String value = entry.getValue();
    System.out.println(key + ": " + value);
}

Example of TreeMap

Here is an example that shows how to use TreeMap to store student grades:

import java.util.TreeMap;

public class TreeMapExample {
    public static void main(String[] args) {
        TreeMap<String, Double> grades = new TreeMap<>();

        // Adding grades
        grades.put("Alice", 90.0);
        grades.put("Bob", 80.0);
        grades.put("Charlie", 95.0);

        // Updating a grade
        grades.put("Bob", 85.0);

        // Removing a grade
        grades.remove("Charlie");

        // Printing grades
        for (String name : grades.keySet()) {
            System.out.println(name + ": " + grades.get(name));
        }
    }
}

Output:

Alice: 90.0
Bob: 85.0