TreeMap in Java are containers that store elements in a mapped fashion that is key-value and mapped value pair. Every element has a key–value and a respective mapped value. All the key values are unique and it is necessary that no two mapped values can have the same key value. It is based on Red-Black Tree implementation in which it does not matter in which order values are inserted in TreeMap, they remain sorted according to their key, unlike HashMap.
Syntax of TreeMap:
TreeMap<Integer, String> tree_map= new TreeMap<Integer, String>();
Syntax of SubMap:
Case 1: Method will include starting key but not include ending key
tree_map.submap(starting_key, ending_key);
Case 2: To include both keys, pass true with keys
tree_map.submap(starting_key, true, ending_key, true);
Case 3: To exclude any key, pass false with key
tree_map.submap(starting_key, false, ending_key, true);
Methods:
- Brute force method
- Using a predefined function
- Using defined comparator
- Using user-defined comparator
Method 1: Printing Default Sorted SubMap
Java
// Java Program to Get Sorted Sub-Map from TreeMap// Importing all classes of// java.util packageimport java.util.*;public class GFG { // Main driver code public static void main(String[] args) { // Create a TreeMap TreeMap<Integer, String> my_map = new TreeMap<Integer, String>(); // Adding Element to TreeMap my_map.put(5, "DoubleAlpha"); my_map.put(1, "Alpha"); my_map.put(3, "Beta"); my_map.put(2, "Gamma"); my_map.put(4, "Theta"); // Printing default sorted elements in given range // using subMap function System.out.println( "Elements: " + my_map.subMap(1, true, 5, true)); }} |
Elements: {1=Alpha, 2=Gamma, 3=Beta, 4=Theta, 5=DoubleAlpha}
Method 2: Reversed sorted Map using predefined functions
Example:
Java
// Java Program to Get Sorted Sub-Map from TreeMap// using predefined functions// Importing all classes of// java.util packageimport java.util.*;public class GFG { // Main driver code public static void main(String[] args) { // Create a TreeMap TreeMap<Integer, String> my_map = new TreeMap<Integer, String>(); // Adding elements to TreeMap my_map.put(5, "DoubleAlpha"); my_map.put(1, "Alpha"); my_map.put(3, "Beta"); my_map.put(2, "Gamma"); my_map.put(4, "Theta"); // Reversing elements of map in // descending order Map<Integer, String> reversed_map = my_map.descendingMap(); // Printing default reverse sorted elements // using subMap() function System.out.println("Elements: " + reversed_map); }} |
Elements: {5=DoubleAlpha, 4=Theta, 3=Beta, 2=Gamma, 1=Alpha}
Method 3: Printing Sorted Sub-Map using User Defined Comparator
The idea behind the user-defined comparator is that if the user wants to sort the map according to the user’s preference. Compare the function of the comparator is used to implement our sorting logic.
Example:
Java
// Java Program to Get Sorted Sub-Map from TreeMap// using user-defined comparator// Importing all classes of// java.util packageimport java.util.*;// Classpublic class GFG { // Main driver Code public static void main(String a[]) { // Sorting TreeMap by key TreeMap<String, String> my_map = new TreeMap<String, String>(new UserComp()); // Add key-value pair to TreeMap my_map.put("DoubleAlpha", "RedDotGeek"); my_map.put("Alpha", "GeekAmongGeek"); my_map.put("Beta", "MasterGeek"); my_map.put("Gamma", "Geek"); my_map.put("Theta", "OnwayGeek"); // Display above added elements of TreeMap System.out.println( "Elements: " + my_map.subMap("A", true, "Z", true)); }}// Pre-defined comparatorclass UserComp implements Comparator<String> { public int compare(String a, String b) { return a.compareTo(b); }} |
Elements: {Alpha=GeekAmongGeek, Beta=MasterGeek, DoubleAlpha=RedDotGeek, Gamma=Geek, Theta=OnwayGeek}
Method 4: Reversed Sorted Map using User Defined Comparator
Java
// Java Program to Get Sorted Sub-Map from TreeMap// using pre-defined comparator// Importing all classes of// java.util packageimport java.util.*;public class GFG { // Main driver method public static void main(String a[]) { // Sorting treeMap by key TreeMap<Integer, String> my_map = new TreeMap<Integer, String>(new UserComp()); // Adding key-value pair to TreeMap my_map.put(1, "DoubleAlpha"); my_map.put(8, "Alpha"); my_map.put(5, "Beta"); my_map.put(3, "Gamma"); my_map.put(4, "Theta"); // Display elements added of TreeMap System.out.println("Elements : " + my_map); }}// Defined comparatorclass UserComp implements Comparator<Integer> { public int compare(Integer a, Integer b) { if (b > a) return 1; return -1; }} |
Elements : {8=Alpha, 5=Beta, 4=Theta, 3=Gamma, 1=DoubleAlpha}
